Import mbedtls-2.16.0

Imports mbedTLS 2.16.0 from https://github.com/ARMmbed/mbedtls.git
commit fb1972db23da ("Merge pull request #544 from ARMmbed/version-2.16")
(tag mbedtls-2.16.0).

Certain files will never be needed and are thus removed (reducing number
of lines to almost 50%):
rm -f circle.yml CMakeLists.txt DartConfiguration.tcl Makefile
rm -f .gitignore .travis.yml .pylint
rm -f include/.gitignore include/CMakeLists.txt library/.gitignore
rm -f library/CMakeLists.txt library/Makefile
rm -rf .git .github doxygen configs programs scripts tests visualc yotta

This is a complete overwrite of previous code so earlier changes in the
branch import/mbedtls-2.6.1 will be added on top of this commit to bring
the changes forward.

Acked-by: Jerome Forissier <jerome.forissier@linaro.org>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>
diff --git a/lib/libmbedtls/mbedtls/library/x509_crt.c b/lib/libmbedtls/mbedtls/library/x509_crt.c
index 43e2d26..7655834 100644
--- a/lib/libmbedtls/mbedtls/library/x509_crt.c
+++ b/lib/libmbedtls/mbedtls/library/x509_crt.c
@@ -1,8 +1,8 @@
-// SPDX-License-Identifier: Apache-2.0
 /*
  *  X.509 certificate parsing and verification
  *
  *  Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
+ *  SPDX-License-Identifier: Apache-2.0
  *
  *  Licensed under the Apache License, Version 2.0 (the "License"); you may
  *  not use this file except in compliance with the License.
@@ -27,6 +27,8 @@
  *
  *  http://www.itu.int/ITU-T/studygroups/com17/languages/X.680-0207.pdf
  *  http://www.itu.int/ITU-T/studygroups/com17/languages/X.690-0207.pdf
+ *
+ *  [SIRO] https://cabforum.org/wp-content/uploads/Chunghwatelecom201503cabforumV4.pdf
  */
 
 #if !defined(MBEDTLS_CONFIG_FILE)
@@ -39,8 +41,8 @@
 
 #include "mbedtls/x509_crt.h"
 #include "mbedtls/oid.h"
+#include "mbedtls/platform_util.h"
 
-#include <stdio.h>
 #include <string.h>
 
 #if defined(MBEDTLS_PEM_PARSE_C)
@@ -50,6 +52,7 @@
 #if defined(MBEDTLS_PLATFORM_C)
 #include "mbedtls/platform.h"
 #else
+#include <stdio.h>
 #include <stdlib.h>
 #define mbedtls_free       free
 #define mbedtls_calloc    calloc
@@ -75,10 +78,18 @@
 #endif /* !_WIN32 || EFIX64 || EFI32 */
 #endif
 
-/* Implementation that should never be optimized out by the compiler */
-static void mbedtls_zeroize( void *v, size_t n ) {
-    volatile unsigned char *p = v; while( n-- ) *p++ = 0;
-}
+/*
+ * Item in a verification chain: cert and flags for it
+ */
+typedef struct {
+    mbedtls_x509_crt *crt;
+    uint32_t flags;
+} x509_crt_verify_chain_item;
+
+/*
+ * Max size of verification chain: end-entity + intermediates + trusted root
+ */
+#define X509_MAX_VERIFY_CHAIN_SIZE    ( MBEDTLS_X509_MAX_INTERMEDIATE_CA + 2 )
 
 /*
  * Default profile
@@ -133,7 +144,8 @@
     MBEDTLS_X509_ID_FLAG( MBEDTLS_MD_SHA256 ) |
     MBEDTLS_X509_ID_FLAG( MBEDTLS_MD_SHA384 ),
     /* Only ECDSA */
-    MBEDTLS_X509_ID_FLAG( MBEDTLS_PK_ECDSA ),
+    MBEDTLS_X509_ID_FLAG( MBEDTLS_PK_ECDSA ) |
+    MBEDTLS_X509_ID_FLAG( MBEDTLS_PK_ECKEY ),
 #if defined(MBEDTLS_ECP_C)
     /* Only NIST P-256 and P-384 */
     MBEDTLS_X509_ID_FLAG( MBEDTLS_ECP_DP_SECP256R1 ) |
@@ -146,11 +158,14 @@
 
 /*
  * Check md_alg against profile
- * Return 0 if md_alg acceptable for this profile, -1 otherwise
+ * Return 0 if md_alg is acceptable for this profile, -1 otherwise
  */
 static int x509_profile_check_md_alg( const mbedtls_x509_crt_profile *profile,
                                       mbedtls_md_type_t md_alg )
 {
+    if( md_alg == MBEDTLS_MD_NONE )
+        return( -1 );
+
     if( ( profile->allowed_mds & MBEDTLS_X509_ID_FLAG( md_alg ) ) != 0 )
         return( 0 );
 
@@ -159,11 +174,14 @@
 
 /*
  * Check pk_alg against profile
- * Return 0 if pk_alg acceptable for this profile, -1 otherwise
+ * Return 0 if pk_alg is acceptable for this profile, -1 otherwise
  */
 static int x509_profile_check_pk_alg( const mbedtls_x509_crt_profile *profile,
                                       mbedtls_pk_type_t pk_alg )
 {
+    if( pk_alg == MBEDTLS_PK_NONE )
+        return( -1 );
+
     if( ( profile->allowed_pks & MBEDTLS_X509_ID_FLAG( pk_alg ) ) != 0 )
         return( 0 );
 
@@ -172,12 +190,13 @@
 
 /*
  * Check key against profile
- * Return 0 if pk_alg acceptable for this profile, -1 otherwise
+ * Return 0 if pk is acceptable for this profile, -1 otherwise
  */
 static int x509_profile_check_key( const mbedtls_x509_crt_profile *profile,
-                                   mbedtls_pk_type_t pk_alg,
                                    const mbedtls_pk_context *pk )
 {
+    const mbedtls_pk_type_t pk_alg = mbedtls_pk_get_type( pk );
+
 #if defined(MBEDTLS_RSA_C)
     if( pk_alg == MBEDTLS_PK_RSA || pk_alg == MBEDTLS_PK_RSASSA_PSS )
     {
@@ -193,7 +212,10 @@
         pk_alg == MBEDTLS_PK_ECKEY ||
         pk_alg == MBEDTLS_PK_ECKEY_DH )
     {
-        mbedtls_ecp_group_id gid = mbedtls_pk_ec( *pk )->grp.id;
+        const mbedtls_ecp_group_id gid = mbedtls_pk_ec( *pk )->grp.id;
+
+        if( gid == MBEDTLS_ECP_DP_NONE )
+            return( -1 );
 
         if( ( profile->allowed_curves & MBEDTLS_X509_ID_FLAG( gid ) ) != 0 )
             return( 0 );
@@ -206,6 +228,153 @@
 }
 
 /*
+ * Like memcmp, but case-insensitive and always returns -1 if different
+ */
+static int x509_memcasecmp( const void *s1, const void *s2, size_t len )
+{
+    size_t i;
+    unsigned char diff;
+    const unsigned char *n1 = s1, *n2 = s2;
+
+    for( i = 0; i < len; i++ )
+    {
+        diff = n1[i] ^ n2[i];
+
+        if( diff == 0 )
+            continue;
+
+        if( diff == 32 &&
+            ( ( n1[i] >= 'a' && n1[i] <= 'z' ) ||
+              ( n1[i] >= 'A' && n1[i] <= 'Z' ) ) )
+        {
+            continue;
+        }
+
+        return( -1 );
+    }
+
+    return( 0 );
+}
+
+/*
+ * Return 0 if name matches wildcard, -1 otherwise
+ */
+static int x509_check_wildcard( const char *cn, const mbedtls_x509_buf *name )
+{
+    size_t i;
+    size_t cn_idx = 0, cn_len = strlen( cn );
+
+    /* We can't have a match if there is no wildcard to match */
+    if( name->len < 3 || name->p[0] != '*' || name->p[1] != '.' )
+        return( -1 );
+
+    for( i = 0; i < cn_len; ++i )
+    {
+        if( cn[i] == '.' )
+        {
+            cn_idx = i;
+            break;
+        }
+    }
+
+    if( cn_idx == 0 )
+        return( -1 );
+
+    if( cn_len - cn_idx == name->len - 1 &&
+        x509_memcasecmp( name->p + 1, cn + cn_idx, name->len - 1 ) == 0 )
+    {
+        return( 0 );
+    }
+
+    return( -1 );
+}
+
+/*
+ * Compare two X.509 strings, case-insensitive, and allowing for some encoding
+ * variations (but not all).
+ *
+ * Return 0 if equal, -1 otherwise.
+ */
+static int x509_string_cmp( const mbedtls_x509_buf *a, const mbedtls_x509_buf *b )
+{
+    if( a->tag == b->tag &&
+        a->len == b->len &&
+        memcmp( a->p, b->p, b->len ) == 0 )
+    {
+        return( 0 );
+    }
+
+    if( ( a->tag == MBEDTLS_ASN1_UTF8_STRING || a->tag == MBEDTLS_ASN1_PRINTABLE_STRING ) &&
+        ( b->tag == MBEDTLS_ASN1_UTF8_STRING || b->tag == MBEDTLS_ASN1_PRINTABLE_STRING ) &&
+        a->len == b->len &&
+        x509_memcasecmp( a->p, b->p, b->len ) == 0 )
+    {
+        return( 0 );
+    }
+
+    return( -1 );
+}
+
+/*
+ * Compare two X.509 Names (aka rdnSequence).
+ *
+ * See RFC 5280 section 7.1, though we don't implement the whole algorithm:
+ * we sometimes return unequal when the full algorithm would return equal,
+ * but never the other way. (In particular, we don't do Unicode normalisation
+ * or space folding.)
+ *
+ * Return 0 if equal, -1 otherwise.
+ */
+static int x509_name_cmp( const mbedtls_x509_name *a, const mbedtls_x509_name *b )
+{
+    /* Avoid recursion, it might not be optimised by the compiler */
+    while( a != NULL || b != NULL )
+    {
+        if( a == NULL || b == NULL )
+            return( -1 );
+
+        /* type */
+        if( a->oid.tag != b->oid.tag ||
+            a->oid.len != b->oid.len ||
+            memcmp( a->oid.p, b->oid.p, b->oid.len ) != 0 )
+        {
+            return( -1 );
+        }
+
+        /* value */
+        if( x509_string_cmp( &a->val, &b->val ) != 0 )
+            return( -1 );
+
+        /* structure of the list of sets */
+        if( a->next_merged != b->next_merged )
+            return( -1 );
+
+        a = a->next;
+        b = b->next;
+    }
+
+    /* a == NULL == b */
+    return( 0 );
+}
+
+/*
+ * Reset (init or clear) a verify_chain
+ */
+static void x509_crt_verify_chain_reset(
+    mbedtls_x509_crt_verify_chain *ver_chain )
+{
+    size_t i;
+
+    for( i = 0; i < MBEDTLS_X509_MAX_VERIFY_CHAIN_SIZE; i++ )
+    {
+        ver_chain->items[i].crt = NULL;
+        ver_chain->items[i].flags = -1;
+    }
+
+    ver_chain->len = 0;
+}
+
+/*
  *  Version  ::=  INTEGER  {  v1(0), v2(1), v3(2)  }
  */
 static int x509_get_version( unsigned char **p,
@@ -472,9 +641,12 @@
         if( ( ret = mbedtls_asn1_get_len( p, end, &tag_len ) ) != 0 )
             return( MBEDTLS_ERR_X509_INVALID_EXTENSIONS + ret );
 
-        if( ( tag & MBEDTLS_ASN1_CONTEXT_SPECIFIC ) != MBEDTLS_ASN1_CONTEXT_SPECIFIC )
+        if( ( tag & MBEDTLS_ASN1_TAG_CLASS_MASK ) !=
+                MBEDTLS_ASN1_CONTEXT_SPECIFIC )
+        {
             return( MBEDTLS_ERR_X509_INVALID_EXTENSIONS +
                     MBEDTLS_ERR_ASN1_UNEXPECTED_TAG );
+        }
 
         /* Skip everything but DNS name */
         if( tag != ( MBEDTLS_ASN1_CONTEXT_SPECIFIC | 2 ) )
@@ -554,18 +726,14 @@
         end_ext_data = *p + len;
 
         /* Get extension ID */
-        extn_oid.tag = **p;
-
-        if( ( ret = mbedtls_asn1_get_tag( p, end, &extn_oid.len, MBEDTLS_ASN1_OID ) ) != 0 )
+        if( ( ret = mbedtls_asn1_get_tag( p, end_ext_data, &extn_oid.len,
+                                          MBEDTLS_ASN1_OID ) ) != 0 )
             return( MBEDTLS_ERR_X509_INVALID_EXTENSIONS + ret );
 
+        extn_oid.tag = MBEDTLS_ASN1_OID;
         extn_oid.p = *p;
         *p += extn_oid.len;
 
-        if( ( end - *p ) < 1 )
-            return( MBEDTLS_ERR_X509_INVALID_EXTENSIONS +
-                    MBEDTLS_ERR_ASN1_OUT_OF_DATA );
-
         /* Get optional critical */
         if( ( ret = mbedtls_asn1_get_bool( p, end_ext_data, &is_critical ) ) != 0 &&
             ( ret != MBEDTLS_ERR_ASN1_UNEXPECTED_TAG ) )
@@ -713,7 +881,7 @@
 
     memcpy( p, buf, crt->raw.len );
 
-    // Direct pointers to the new buffer 
+    // Direct pointers to the new buffer
     p += crt->raw.len - len;
     end = crt_end = p + len;
 
@@ -1095,7 +1263,7 @@
 
     ret = mbedtls_x509_crt_parse( chain, buf, n );
 
-    mbedtls_zeroize( buf, n );
+    mbedtls_platform_zeroize( buf, n );
     mbedtls_free( buf );
 
     return( ret );
@@ -1630,7 +1798,7 @@
 
 /*
  * Check that the given certificate is not revoked according to the CRL.
- * Skip validation is no CRL for the given CA is present.
+ * Skip validation if no CRL for the given CA is present.
  */
 static int x509_crt_verifycrl( mbedtls_x509_crt *crt, mbedtls_x509_crt *ca,
                                mbedtls_x509_crl *crl_list,
@@ -1646,9 +1814,7 @@
     while( crl_list != NULL )
     {
         if( crl_list->version == 0 ||
-            crl_list->issuer_raw.len != ca->subject_raw.len ||
-            memcmp( crl_list->issuer_raw.p, ca->subject_raw.p,
-                    crl_list->issuer_raw.len ) != 0 )
+            x509_name_cmp( &crl_list->issuer, &ca->subject ) != 0 )
         {
             crl_list = crl_list->next;
             continue;
@@ -1658,7 +1824,8 @@
          * Check if the CA is configured to sign CRLs
          */
 #if defined(MBEDTLS_X509_CHECK_KEY_USAGE)
-        if( mbedtls_x509_crt_check_key_usage( ca, MBEDTLS_X509_KU_CRL_SIGN ) != 0 )
+        if( mbedtls_x509_crt_check_key_usage( ca,
+                                              MBEDTLS_X509_KU_CRL_SIGN ) != 0 )
         {
             flags |= MBEDTLS_X509_BADCRL_NOT_TRUSTED;
             break;
@@ -1675,18 +1842,14 @@
             flags |= MBEDTLS_X509_BADCRL_BAD_PK;
 
         md_info = mbedtls_md_info_from_type( crl_list->sig_md );
-        if( md_info == NULL )
+        if( mbedtls_md( md_info, crl_list->tbs.p, crl_list->tbs.len, hash ) != 0 )
         {
-            /*
-             * Cannot check 'unknown' hash
-             */
+            /* Note: this can't happen except after an internal error */
             flags |= MBEDTLS_X509_BADCRL_NOT_TRUSTED;
             break;
         }
 
-        mbedtls_md( md_info, crl_list->tbs.p, crl_list->tbs.len, hash );
-
-        if( x509_profile_check_key( profile, crl_list->sig_pk, &ca->pk ) != 0 )
+        if( x509_profile_check_key( profile, &ca->pk ) != 0 )
             flags |= MBEDTLS_X509_BADCERT_BAD_KEY;
 
         if( mbedtls_pk_verify_ext( crl_list->sig_pk, crl_list->sig_opts, &ca->pk,
@@ -1723,132 +1886,40 @@
 #endif /* MBEDTLS_X509_CRL_PARSE_C */
 
 /*
- * Like memcmp, but case-insensitive and always returns -1 if different
+ * Check the signature of a certificate by its parent
  */
-static int x509_memcasecmp( const void *s1, const void *s2, size_t len )
+static int x509_crt_check_signature( const mbedtls_x509_crt *child,
+                                     mbedtls_x509_crt *parent,
+                                     mbedtls_x509_crt_restart_ctx *rs_ctx )
 {
-    size_t i;
-    unsigned char diff;
-    const unsigned char *n1 = s1, *n2 = s2;
+    const mbedtls_md_info_t *md_info;
+    unsigned char hash[MBEDTLS_MD_MAX_SIZE];
 
-    for( i = 0; i < len; i++ )
+    md_info = mbedtls_md_info_from_type( child->sig_md );
+    if( mbedtls_md( md_info, child->tbs.p, child->tbs.len, hash ) != 0 )
     {
-        diff = n1[i] ^ n2[i];
-
-        if( diff == 0 )
-            continue;
-
-        if( diff == 32 &&
-            ( ( n1[i] >= 'a' && n1[i] <= 'z' ) ||
-              ( n1[i] >= 'A' && n1[i] <= 'Z' ) ) )
-        {
-            continue;
-        }
-
+        /* Note: this can't happen except after an internal error */
         return( -1 );
     }
 
-    return( 0 );
-}
-
-/*
- * Return 0 if name matches wildcard, -1 otherwise
- */
-static int x509_check_wildcard( const char *cn, mbedtls_x509_buf *name )
-{
-    size_t i;
-    size_t cn_idx = 0, cn_len = strlen( cn );
-
-    if( name->len < 3 || name->p[0] != '*' || name->p[1] != '.' )
-        return( 0 );
-
-    for( i = 0; i < cn_len; ++i )
-    {
-        if( cn[i] == '.' )
-        {
-            cn_idx = i;
-            break;
-        }
-    }
-
-    if( cn_idx == 0 )
+    /* Skip expensive computation on obvious mismatch */
+    if( ! mbedtls_pk_can_do( &parent->pk, child->sig_pk ) )
         return( -1 );
 
-    if( cn_len - cn_idx == name->len - 1 &&
-        x509_memcasecmp( name->p + 1, cn + cn_idx, name->len - 1 ) == 0 )
+#if defined(MBEDTLS_ECDSA_C) && defined(MBEDTLS_ECP_RESTARTABLE)
+    if( rs_ctx != NULL && child->sig_pk == MBEDTLS_PK_ECDSA )
     {
-        return( 0 );
+        return( mbedtls_pk_verify_restartable( &parent->pk,
+                    child->sig_md, hash, mbedtls_md_get_size( md_info ),
+                    child->sig.p, child->sig.len, &rs_ctx->pk ) );
     }
+#else
+    (void) rs_ctx;
+#endif
 
-    return( -1 );
-}
-
-/*
- * Compare two X.509 strings, case-insensitive, and allowing for some encoding
- * variations (but not all).
- *
- * Return 0 if equal, -1 otherwise.
- */
-static int x509_string_cmp( const mbedtls_x509_buf *a, const mbedtls_x509_buf *b )
-{
-    if( a->tag == b->tag &&
-        a->len == b->len &&
-        memcmp( a->p, b->p, b->len ) == 0 )
-    {
-        return( 0 );
-    }
-
-    if( ( a->tag == MBEDTLS_ASN1_UTF8_STRING || a->tag == MBEDTLS_ASN1_PRINTABLE_STRING ) &&
-        ( b->tag == MBEDTLS_ASN1_UTF8_STRING || b->tag == MBEDTLS_ASN1_PRINTABLE_STRING ) &&
-        a->len == b->len &&
-        x509_memcasecmp( a->p, b->p, b->len ) == 0 )
-    {
-        return( 0 );
-    }
-
-    return( -1 );
-}
-
-/*
- * Compare two X.509 Names (aka rdnSequence).
- *
- * See RFC 5280 section 7.1, though we don't implement the whole algorithm:
- * we sometimes return unequal when the full algorithm would return equal,
- * but never the other way. (In particular, we don't do Unicode normalisation
- * or space folding.)
- *
- * Return 0 if equal, -1 otherwise.
- */
-static int x509_name_cmp( const mbedtls_x509_name *a, const mbedtls_x509_name *b )
-{
-    /* Avoid recursion, it might not be optimised by the compiler */
-    while( a != NULL || b != NULL )
-    {
-        if( a == NULL || b == NULL )
-            return( -1 );
-
-        /* type */
-        if( a->oid.tag != b->oid.tag ||
-            a->oid.len != b->oid.len ||
-            memcmp( a->oid.p, b->oid.p, b->oid.len ) != 0 )
-        {
-            return( -1 );
-        }
-
-        /* value */
-        if( x509_string_cmp( &a->val, &b->val ) != 0 )
-            return( -1 );
-
-        /* structure of the list of sets */
-        if( a->next_merged != b->next_merged )
-            return( -1 );
-
-        a = a->next;
-        b = b->next;
-    }
-
-    /* a == NULL == b */
-    return( 0 );
+    return( mbedtls_pk_verify_ext( child->sig_pk, child->sig_opts, &parent->pk,
+                child->sig_md, hash, mbedtls_md_get_size( md_info ),
+                child->sig.p, child->sig.len ) );
 }
 
 /*
@@ -1856,11 +1927,10 @@
  * Return 0 if yes, -1 if not.
  *
  * top means parent is a locally-trusted certificate
- * bottom means child is the end entity cert
  */
 static int x509_crt_check_parent( const mbedtls_x509_crt *child,
                                   const mbedtls_x509_crt *parent,
-                                  int top, int bottom )
+                                  int top )
 {
     int need_ca_bit;
 
@@ -1875,14 +1945,6 @@
     if( top && parent->version < 3 )
         need_ca_bit = 0;
 
-    /* Exception: self-signed end-entity certs that are locally trusted. */
-    if( top && bottom &&
-        child->raw.len == parent->raw.len &&
-        memcmp( child->raw.p, parent->raw.p, child->raw.len ) == 0 )
-    {
-        need_ca_bit = 0;
-    }
-
     if( need_ca_bit && ! parent->ca_istrue )
         return( -1 );
 
@@ -1897,86 +1959,131 @@
     return( 0 );
 }
 
-static int x509_crt_verify_top(
-                mbedtls_x509_crt *child, mbedtls_x509_crt *trust_ca,
-                mbedtls_x509_crl *ca_crl,
-                const mbedtls_x509_crt_profile *profile,
-                int path_cnt, int self_cnt, uint32_t *flags,
-                int (*f_vrfy)(void *, mbedtls_x509_crt *, int, uint32_t *),
-                void *p_vrfy )
+/*
+ * Find a suitable parent for child in candidates, or return NULL.
+ *
+ * Here suitable is defined as:
+ *  1. subject name matches child's issuer
+ *  2. if necessary, the CA bit is set and key usage allows signing certs
+ *  3. for trusted roots, the signature is correct
+ *     (for intermediates, the signature is checked and the result reported)
+ *  4. pathlen constraints are satisfied
+ *
+ * If there's a suitable candidate which is also time-valid, return the first
+ * such. Otherwise, return the first suitable candidate (or NULL if there is
+ * none).
+ *
+ * The rationale for this rule is that someone could have a list of trusted
+ * roots with two versions on the same root with different validity periods.
+ * (At least one user reported having such a list and wanted it to just work.)
+ * The reason we don't just require time-validity is that generally there is
+ * only one version, and if it's expired we want the flags to state that
+ * rather than NOT_TRUSTED, as would be the case if we required it here.
+ *
+ * The rationale for rule 3 (signature for trusted roots) is that users might
+ * have two versions of the same CA with different keys in their list, and the
+ * way we select the correct one is by checking the signature (as we don't
+ * rely on key identifier extensions). (This is one way users might choose to
+ * handle key rollover, another relies on self-issued certs, see [SIRO].)
+ *
+ * Arguments:
+ *  - [in] child: certificate for which we're looking for a parent
+ *  - [in] candidates: chained list of potential parents
+ *  - [out] r_parent: parent found (or NULL)
+ *  - [out] r_signature_is_good: 1 if child signature by parent is valid, or 0
+ *  - [in] top: 1 if candidates consists of trusted roots, ie we're at the top
+ *         of the chain, 0 otherwise
+ *  - [in] path_cnt: number of intermediates seen so far
+ *  - [in] self_cnt: number of self-signed intermediates seen so far
+ *         (will never be greater than path_cnt)
+ *  - [in-out] rs_ctx: context for restarting operations
+ *
+ * Return value:
+ *  - 0 on success
+ *  - MBEDTLS_ERR_ECP_IN_PROGRESS otherwise
+ */
+static int x509_crt_find_parent_in(
+                        mbedtls_x509_crt *child,
+                        mbedtls_x509_crt *candidates,
+                        mbedtls_x509_crt **r_parent,
+                        int *r_signature_is_good,
+                        int top,
+                        unsigned path_cnt,
+                        unsigned self_cnt,
+                        mbedtls_x509_crt_restart_ctx *rs_ctx )
 {
     int ret;
-    uint32_t ca_flags = 0;
-    int check_path_cnt;
-    unsigned char hash[MBEDTLS_MD_MAX_SIZE];
-    const mbedtls_md_info_t *md_info;
-    mbedtls_x509_crt *future_past_ca = NULL;
+    mbedtls_x509_crt *parent, *fallback_parent;
+    int signature_is_good, fallback_signature_is_good;
 
-    if( mbedtls_x509_time_is_past( &child->valid_to ) )
-        *flags |= MBEDTLS_X509_BADCERT_EXPIRED;
-
-    if( mbedtls_x509_time_is_future( &child->valid_from ) )
-        *flags |= MBEDTLS_X509_BADCERT_FUTURE;
-
-    if( x509_profile_check_md_alg( profile, child->sig_md ) != 0 )
-        *flags |= MBEDTLS_X509_BADCERT_BAD_MD;
-
-    if( x509_profile_check_pk_alg( profile, child->sig_pk ) != 0 )
-        *flags |= MBEDTLS_X509_BADCERT_BAD_PK;
-
-    /*
-     * Child is the top of the chain. Check against the trust_ca list.
-     */
-    *flags |= MBEDTLS_X509_BADCERT_NOT_TRUSTED;
-
-    md_info = mbedtls_md_info_from_type( child->sig_md );
-    if( md_info == NULL )
+#if defined(MBEDTLS_ECDSA_C) && defined(MBEDTLS_ECP_RESTARTABLE)
+    /* did we have something in progress? */
+    if( rs_ctx != NULL && rs_ctx->parent != NULL )
     {
-        /*
-         * Cannot check 'unknown', no need to try any CA
-         */
-        trust_ca = NULL;
+        /* restore saved state */
+        parent = rs_ctx->parent;
+        fallback_parent = rs_ctx->fallback_parent;
+        fallback_signature_is_good = rs_ctx->fallback_signature_is_good;
+
+        /* clear saved state */
+        rs_ctx->parent = NULL;
+        rs_ctx->fallback_parent = NULL;
+        rs_ctx->fallback_signature_is_good = 0;
+
+        /* resume where we left */
+        goto check_signature;
     }
-    else
-        mbedtls_md( md_info, child->tbs.p, child->tbs.len, hash );
+#endif
 
-    for( /* trust_ca */ ; trust_ca != NULL; trust_ca = trust_ca->next )
+    fallback_parent = NULL;
+    fallback_signature_is_good = 0;
+
+    for( parent = candidates; parent != NULL; parent = parent->next )
     {
-        if( x509_crt_check_parent( child, trust_ca, 1, path_cnt == 0 ) != 0 )
+        /* basic parenting skills (name, CA bit, key usage) */
+        if( x509_crt_check_parent( child, parent, top ) != 0 )
             continue;
 
-        check_path_cnt = path_cnt + 1;
-
-        /*
-         * Reduce check_path_cnt to check against if top of the chain is
-         * the same as the trusted CA
-         */
-        if( child->subject_raw.len == trust_ca->subject_raw.len &&
-            memcmp( child->subject_raw.p, trust_ca->subject_raw.p,
-                            child->issuer_raw.len ) == 0 )
-        {
-            check_path_cnt--;
-        }
-
-        /* Self signed certificates do not count towards the limit */
-        if( trust_ca->max_pathlen > 0 &&
-            trust_ca->max_pathlen < check_path_cnt - self_cnt )
+        /* +1 because stored max_pathlen is 1 higher that the actual value */
+        if( parent->max_pathlen > 0 &&
+            (size_t) parent->max_pathlen < 1 + path_cnt - self_cnt )
         {
             continue;
         }
 
-        if( mbedtls_pk_verify_ext( child->sig_pk, child->sig_opts, &trust_ca->pk,
-                           child->sig_md, hash, mbedtls_md_get_size( md_info ),
-                           child->sig.p, child->sig.len ) != 0 )
-        {
-            continue;
-        }
+        /* Signature */
+#if defined(MBEDTLS_ECDSA_C) && defined(MBEDTLS_ECP_RESTARTABLE)
+check_signature:
+#endif
+        ret = x509_crt_check_signature( child, parent, rs_ctx );
 
-        if( mbedtls_x509_time_is_past( &trust_ca->valid_to ) ||
-            mbedtls_x509_time_is_future( &trust_ca->valid_from ) )
+#if defined(MBEDTLS_ECDSA_C) && defined(MBEDTLS_ECP_RESTARTABLE)
+        if( rs_ctx != NULL && ret == MBEDTLS_ERR_ECP_IN_PROGRESS )
         {
-            if ( future_past_ca == NULL )
-                future_past_ca = trust_ca;
+            /* save state */
+            rs_ctx->parent = parent;
+            rs_ctx->fallback_parent = fallback_parent;
+            rs_ctx->fallback_signature_is_good = fallback_signature_is_good;
+
+            return( ret );
+        }
+#else
+        (void) ret;
+#endif
+
+        signature_is_good = ret == 0;
+        if( top && ! signature_is_good )
+            continue;
+
+        /* optional time check */
+        if( mbedtls_x509_time_is_past( &parent->valid_to ) ||
+            mbedtls_x509_time_is_future( &parent->valid_from ) )
+        {
+            if( fallback_parent == NULL )
+            {
+                fallback_parent = parent;
+                fallback_signature_is_good = signature_is_good;
+            }
 
             continue;
         }
@@ -1984,196 +2091,409 @@
         break;
     }
 
-    if( trust_ca != NULL || ( trust_ca = future_past_ca ) != NULL )
+    if( parent != NULL )
     {
-        /*
-         * Top of chain is signed by a trusted CA
-         */
-        *flags &= ~MBEDTLS_X509_BADCERT_NOT_TRUSTED;
-
-        if( x509_profile_check_key( profile, child->sig_pk, &trust_ca->pk ) != 0 )
-            *flags |= MBEDTLS_X509_BADCERT_BAD_KEY;
-    }
-
-    /*
-     * If top of chain is not the same as the trusted CA send a verify request
-     * to the callback for any issues with validity and CRL presence for the
-     * trusted CA certificate.
-     */
-    if( trust_ca != NULL &&
-        ( child->subject_raw.len != trust_ca->subject_raw.len ||
-          memcmp( child->subject_raw.p, trust_ca->subject_raw.p,
-                            child->issuer_raw.len ) != 0 ) )
-    {
-#if defined(MBEDTLS_X509_CRL_PARSE_C)
-        /* Check trusted CA's CRL for the chain's top crt */
-        *flags |= x509_crt_verifycrl( child, trust_ca, ca_crl, profile );
-#else
-        ((void) ca_crl);
-#endif
-
-        if( mbedtls_x509_time_is_past( &trust_ca->valid_to ) )
-            ca_flags |= MBEDTLS_X509_BADCERT_EXPIRED;
-
-        if( mbedtls_x509_time_is_future( &trust_ca->valid_from ) )
-            ca_flags |= MBEDTLS_X509_BADCERT_FUTURE;
-
-        if( NULL != f_vrfy )
-        {
-            if( ( ret = f_vrfy( p_vrfy, trust_ca, path_cnt + 1,
-                                &ca_flags ) ) != 0 )
-            {
-                return( ret );
-            }
-        }
-    }
-
-    /* Call callback on top cert */
-    if( NULL != f_vrfy )
-    {
-        if( ( ret = f_vrfy( p_vrfy, child, path_cnt, flags ) ) != 0 )
-            return( ret );
-    }
-
-    *flags |= ca_flags;
-
-    return( 0 );
-}
-
-static int x509_crt_verify_child(
-                mbedtls_x509_crt *child, mbedtls_x509_crt *parent,
-                mbedtls_x509_crt *trust_ca, mbedtls_x509_crl *ca_crl,
-                const mbedtls_x509_crt_profile *profile,
-                int path_cnt, int self_cnt, uint32_t *flags,
-                int (*f_vrfy)(void *, mbedtls_x509_crt *, int, uint32_t *),
-                void *p_vrfy )
-{
-    int ret;
-    uint32_t parent_flags = 0;
-    unsigned char hash[MBEDTLS_MD_MAX_SIZE];
-    mbedtls_x509_crt *grandparent;
-    const mbedtls_md_info_t *md_info;
-
-    /* Counting intermediate self signed certificates */
-    if( ( path_cnt != 0 ) && x509_name_cmp( &child->issuer, &child->subject ) == 0 )
-        self_cnt++;
-
-    /* path_cnt is 0 for the first intermediate CA */
-    if( 1 + path_cnt > MBEDTLS_X509_MAX_INTERMEDIATE_CA )
-    {
-        /* return immediately as the goal is to avoid unbounded recursion */
-        return( MBEDTLS_ERR_X509_FATAL_ERROR );
-    }
-
-    if( mbedtls_x509_time_is_past( &child->valid_to ) )
-        *flags |= MBEDTLS_X509_BADCERT_EXPIRED;
-
-    if( mbedtls_x509_time_is_future( &child->valid_from ) )
-        *flags |= MBEDTLS_X509_BADCERT_FUTURE;
-
-    if( x509_profile_check_md_alg( profile, child->sig_md ) != 0 )
-        *flags |= MBEDTLS_X509_BADCERT_BAD_MD;
-
-    if( x509_profile_check_pk_alg( profile, child->sig_pk ) != 0 )
-        *flags |= MBEDTLS_X509_BADCERT_BAD_PK;
-
-    md_info = mbedtls_md_info_from_type( child->sig_md );
-    if( md_info == NULL )
-    {
-        /*
-         * Cannot check 'unknown' hash
-         */
-        *flags |= MBEDTLS_X509_BADCERT_NOT_TRUSTED;
+        *r_parent = parent;
+        *r_signature_is_good = signature_is_good;
     }
     else
     {
-        mbedtls_md( md_info, child->tbs.p, child->tbs.len, hash );
-
-        if( x509_profile_check_key( profile, child->sig_pk, &parent->pk ) != 0 )
-            *flags |= MBEDTLS_X509_BADCERT_BAD_KEY;
-
-        if( mbedtls_pk_verify_ext( child->sig_pk, child->sig_opts, &parent->pk,
-                           child->sig_md, hash, mbedtls_md_get_size( md_info ),
-                           child->sig.p, child->sig.len ) != 0 )
-        {
-            *flags |= MBEDTLS_X509_BADCERT_NOT_TRUSTED;
-        }
+        *r_parent = fallback_parent;
+        *r_signature_is_good = fallback_signature_is_good;
     }
 
-#if defined(MBEDTLS_X509_CRL_PARSE_C)
-    /* Check trusted CA's CRL for the given crt */
-    *flags |= x509_crt_verifycrl(child, parent, ca_crl, profile );
-#endif
-
-    /* Look for a grandparent in trusted CAs */
-    for( grandparent = trust_ca;
-         grandparent != NULL;
-         grandparent = grandparent->next )
-    {
-        if( x509_crt_check_parent( parent, grandparent,
-                                   0, path_cnt == 0 ) == 0 )
-            break;
-    }
-
-    if( grandparent != NULL )
-    {
-        ret = x509_crt_verify_top( parent, grandparent, ca_crl, profile,
-                                path_cnt + 1, self_cnt, &parent_flags, f_vrfy, p_vrfy );
-        if( ret != 0 )
-            return( ret );
-    }
-    else
-    {
-        /* Look for a grandparent upwards the chain */
-        for( grandparent = parent->next;
-             grandparent != NULL;
-             grandparent = grandparent->next )
-        {
-            /* +2 because the current step is not yet accounted for
-             * and because max_pathlen is one higher than it should be.
-             * Also self signed certificates do not count to the limit. */
-            if( grandparent->max_pathlen > 0 &&
-                grandparent->max_pathlen < 2 + path_cnt - self_cnt )
-            {
-                continue;
-            }
-
-            if( x509_crt_check_parent( parent, grandparent,
-                                       0, path_cnt == 0 ) == 0 )
-                break;
-        }
-
-        /* Is our parent part of the chain or at the top? */
-        if( grandparent != NULL )
-        {
-            ret = x509_crt_verify_child( parent, grandparent, trust_ca, ca_crl,
-                                         profile, path_cnt + 1, self_cnt, &parent_flags,
-                                         f_vrfy, p_vrfy );
-            if( ret != 0 )
-                return( ret );
-        }
-        else
-        {
-            ret = x509_crt_verify_top( parent, trust_ca, ca_crl, profile,
-                                       path_cnt + 1, self_cnt, &parent_flags,
-                                       f_vrfy, p_vrfy );
-            if( ret != 0 )
-                return( ret );
-        }
-    }
-
-    /* child is verified to be a child of the parent, call verify callback */
-    if( NULL != f_vrfy )
-        if( ( ret = f_vrfy( p_vrfy, child, path_cnt, flags ) ) != 0 )
-            return( ret );
-
-    *flags |= parent_flags;
-
     return( 0 );
 }
 
 /*
- * Verify the certificate validity
+ * Find a parent in trusted CAs or the provided chain, or return NULL.
+ *
+ * Searches in trusted CAs first, and return the first suitable parent found
+ * (see find_parent_in() for definition of suitable).
+ *
+ * Arguments:
+ *  - [in] child: certificate for which we're looking for a parent, followed
+ *         by a chain of possible intermediates
+ *  - [in] trust_ca: list of locally trusted certificates
+ *  - [out] parent: parent found (or NULL)
+ *  - [out] parent_is_trusted: 1 if returned `parent` is trusted, or 0
+ *  - [out] signature_is_good: 1 if child signature by parent is valid, or 0
+ *  - [in] path_cnt: number of links in the chain so far (EE -> ... -> child)
+ *  - [in] self_cnt: number of self-signed certs in the chain so far
+ *         (will always be no greater than path_cnt)
+ *  - [in-out] rs_ctx: context for restarting operations
+ *
+ * Return value:
+ *  - 0 on success
+ *  - MBEDTLS_ERR_ECP_IN_PROGRESS otherwise
+ */
+static int x509_crt_find_parent(
+                        mbedtls_x509_crt *child,
+                        mbedtls_x509_crt *trust_ca,
+                        mbedtls_x509_crt **parent,
+                        int *parent_is_trusted,
+                        int *signature_is_good,
+                        unsigned path_cnt,
+                        unsigned self_cnt,
+                        mbedtls_x509_crt_restart_ctx *rs_ctx )
+{
+    int ret;
+    mbedtls_x509_crt *search_list;
+
+    *parent_is_trusted = 1;
+
+#if defined(MBEDTLS_ECDSA_C) && defined(MBEDTLS_ECP_RESTARTABLE)
+    /* restore then clear saved state if we have some stored */
+    if( rs_ctx != NULL && rs_ctx->parent_is_trusted != -1 )
+    {
+        *parent_is_trusted = rs_ctx->parent_is_trusted;
+        rs_ctx->parent_is_trusted = -1;
+    }
+#endif
+
+    while( 1 ) {
+        search_list = *parent_is_trusted ? trust_ca : child->next;
+
+        ret = x509_crt_find_parent_in( child, search_list,
+                                       parent, signature_is_good,
+                                       *parent_is_trusted,
+                                       path_cnt, self_cnt, rs_ctx );
+
+#if defined(MBEDTLS_ECDSA_C) && defined(MBEDTLS_ECP_RESTARTABLE)
+        if( rs_ctx != NULL && ret == MBEDTLS_ERR_ECP_IN_PROGRESS )
+        {
+            /* save state */
+            rs_ctx->parent_is_trusted = *parent_is_trusted;
+            return( ret );
+        }
+#else
+        (void) ret;
+#endif
+
+        /* stop here if found or already in second iteration */
+        if( *parent != NULL || *parent_is_trusted == 0 )
+            break;
+
+        /* prepare second iteration */
+        *parent_is_trusted = 0;
+    }
+
+    /* extra precaution against mistakes in the caller */
+    if( *parent == NULL )
+    {
+        *parent_is_trusted = 0;
+        *signature_is_good = 0;
+    }
+
+    return( 0 );
+}
+
+/*
+ * Check if an end-entity certificate is locally trusted
+ *
+ * Currently we require such certificates to be self-signed (actually only
+ * check for self-issued as self-signatures are not checked)
+ */
+static int x509_crt_check_ee_locally_trusted(
+                    mbedtls_x509_crt *crt,
+                    mbedtls_x509_crt *trust_ca )
+{
+    mbedtls_x509_crt *cur;
+
+    /* must be self-issued */
+    if( x509_name_cmp( &crt->issuer, &crt->subject ) != 0 )
+        return( -1 );
+
+    /* look for an exact match with trusted cert */
+    for( cur = trust_ca; cur != NULL; cur = cur->next )
+    {
+        if( crt->raw.len == cur->raw.len &&
+            memcmp( crt->raw.p, cur->raw.p, crt->raw.len ) == 0 )
+        {
+            return( 0 );
+        }
+    }
+
+    /* too bad */
+    return( -1 );
+}
+
+/*
+ * Build and verify a certificate chain
+ *
+ * Given a peer-provided list of certificates EE, C1, ..., Cn and
+ * a list of trusted certs R1, ... Rp, try to build and verify a chain
+ *      EE, Ci1, ... Ciq [, Rj]
+ * such that every cert in the chain is a child of the next one,
+ * jumping to a trusted root as early as possible.
+ *
+ * Verify that chain and return it with flags for all issues found.
+ *
+ * Special cases:
+ * - EE == Rj -> return a one-element list containing it
+ * - EE, Ci1, ..., Ciq cannot be continued with a trusted root
+ *   -> return that chain with NOT_TRUSTED set on Ciq
+ *
+ * Tests for (aspects of) this function should include at least:
+ * - trusted EE
+ * - EE -> trusted root
+ * - EE -> intermedate CA -> trusted root
+ * - if relevant: EE untrusted
+ * - if relevant: EE -> intermediate, untrusted
+ * with the aspect under test checked at each relevant level (EE, int, root).
+ * For some aspects longer chains are required, but usually length 2 is
+ * enough (but length 1 is not in general).
+ *
+ * Arguments:
+ *  - [in] crt: the cert list EE, C1, ..., Cn
+ *  - [in] trust_ca: the trusted list R1, ..., Rp
+ *  - [in] ca_crl, profile: as in verify_with_profile()
+ *  - [out] ver_chain: the built and verified chain
+ *      Only valid when return value is 0, may contain garbage otherwise!
+ *      Restart note: need not be the same when calling again to resume.
+ *  - [in-out] rs_ctx: context for restarting operations
+ *
+ * Return value:
+ *  - non-zero if the chain could not be fully built and examined
+ *  - 0 is the chain was successfully built and examined,
+ *      even if it was found to be invalid
+ */
+static int x509_crt_verify_chain(
+                mbedtls_x509_crt *crt,
+                mbedtls_x509_crt *trust_ca,
+                mbedtls_x509_crl *ca_crl,
+                const mbedtls_x509_crt_profile *profile,
+                mbedtls_x509_crt_verify_chain *ver_chain,
+                mbedtls_x509_crt_restart_ctx *rs_ctx )
+{
+    /* Don't initialize any of those variables here, so that the compiler can
+     * catch potential issues with jumping ahead when restarting */
+    int ret;
+    uint32_t *flags;
+    mbedtls_x509_crt_verify_chain_item *cur;
+    mbedtls_x509_crt *child;
+    mbedtls_x509_crt *parent;
+    int parent_is_trusted;
+    int child_is_trusted;
+    int signature_is_good;
+    unsigned self_cnt;
+
+#if defined(MBEDTLS_ECDSA_C) && defined(MBEDTLS_ECP_RESTARTABLE)
+    /* resume if we had an operation in progress */
+    if( rs_ctx != NULL && rs_ctx->in_progress == x509_crt_rs_find_parent )
+    {
+        /* restore saved state */
+        *ver_chain = rs_ctx->ver_chain; /* struct copy */
+        self_cnt = rs_ctx->self_cnt;
+
+        /* restore derived state */
+        cur = &ver_chain->items[ver_chain->len - 1];
+        child = cur->crt;
+        flags = &cur->flags;
+
+        goto find_parent;
+    }
+#endif /* MBEDTLS_ECDSA_C && MBEDTLS_ECP_RESTARTABLE */
+
+    child = crt;
+    self_cnt = 0;
+    parent_is_trusted = 0;
+    child_is_trusted = 0;
+
+    while( 1 ) {
+        /* Add certificate to the verification chain */
+        cur = &ver_chain->items[ver_chain->len];
+        cur->crt = child;
+        cur->flags = 0;
+        ver_chain->len++;
+        flags = &cur->flags;
+
+        /* Check time-validity (all certificates) */
+        if( mbedtls_x509_time_is_past( &child->valid_to ) )
+            *flags |= MBEDTLS_X509_BADCERT_EXPIRED;
+
+        if( mbedtls_x509_time_is_future( &child->valid_from ) )
+            *flags |= MBEDTLS_X509_BADCERT_FUTURE;
+
+        /* Stop here for trusted roots (but not for trusted EE certs) */
+        if( child_is_trusted )
+            return( 0 );
+
+        /* Check signature algorithm: MD & PK algs */
+        if( x509_profile_check_md_alg( profile, child->sig_md ) != 0 )
+            *flags |= MBEDTLS_X509_BADCERT_BAD_MD;
+
+        if( x509_profile_check_pk_alg( profile, child->sig_pk ) != 0 )
+            *flags |= MBEDTLS_X509_BADCERT_BAD_PK;
+
+        /* Special case: EE certs that are locally trusted */
+        if( ver_chain->len == 1 &&
+            x509_crt_check_ee_locally_trusted( child, trust_ca ) == 0 )
+        {
+            return( 0 );
+        }
+
+#if defined(MBEDTLS_ECDSA_C) && defined(MBEDTLS_ECP_RESTARTABLE)
+find_parent:
+#endif
+        /* Look for a parent in trusted CAs or up the chain */
+        ret = x509_crt_find_parent( child, trust_ca, &parent,
+                                       &parent_is_trusted, &signature_is_good,
+                                       ver_chain->len - 1, self_cnt, rs_ctx );
+
+#if defined(MBEDTLS_ECDSA_C) && defined(MBEDTLS_ECP_RESTARTABLE)
+        if( rs_ctx != NULL && ret == MBEDTLS_ERR_ECP_IN_PROGRESS )
+        {
+            /* save state */
+            rs_ctx->in_progress = x509_crt_rs_find_parent;
+            rs_ctx->self_cnt = self_cnt;
+            rs_ctx->ver_chain = *ver_chain; /* struct copy */
+
+            return( ret );
+        }
+#else
+        (void) ret;
+#endif
+
+        /* No parent? We're done here */
+        if( parent == NULL )
+        {
+            *flags |= MBEDTLS_X509_BADCERT_NOT_TRUSTED;
+            return( 0 );
+        }
+
+        /* Count intermediate self-issued (not necessarily self-signed) certs.
+         * These can occur with some strategies for key rollover, see [SIRO],
+         * and should be excluded from max_pathlen checks. */
+        if( ver_chain->len != 1 &&
+            x509_name_cmp( &child->issuer, &child->subject ) == 0 )
+        {
+            self_cnt++;
+        }
+
+        /* path_cnt is 0 for the first intermediate CA,
+         * and if parent is trusted it's not an intermediate CA */
+        if( ! parent_is_trusted &&
+            ver_chain->len > MBEDTLS_X509_MAX_INTERMEDIATE_CA )
+        {
+            /* return immediately to avoid overflow the chain array */
+            return( MBEDTLS_ERR_X509_FATAL_ERROR );
+        }
+
+        /* signature was checked while searching parent */
+        if( ! signature_is_good )
+            *flags |= MBEDTLS_X509_BADCERT_NOT_TRUSTED;
+
+        /* check size of signing key */
+        if( x509_profile_check_key( profile, &parent->pk ) != 0 )
+            *flags |= MBEDTLS_X509_BADCERT_BAD_KEY;
+
+#if defined(MBEDTLS_X509_CRL_PARSE_C)
+        /* Check trusted CA's CRL for the given crt */
+        *flags |= x509_crt_verifycrl( child, parent, ca_crl, profile );
+#else
+        (void) ca_crl;
+#endif
+
+        /* prepare for next iteration */
+        child = parent;
+        parent = NULL;
+        child_is_trusted = parent_is_trusted;
+        signature_is_good = 0;
+    }
+}
+
+/*
+ * Check for CN match
+ */
+static int x509_crt_check_cn( const mbedtls_x509_buf *name,
+                              const char *cn, size_t cn_len )
+{
+    /* try exact match */
+    if( name->len == cn_len &&
+        x509_memcasecmp( cn, name->p, cn_len ) == 0 )
+    {
+        return( 0 );
+    }
+
+    /* try wildcard match */
+    if( x509_check_wildcard( cn, name ) == 0 )
+    {
+        return( 0 );
+    }
+
+    return( -1 );
+}
+
+/*
+ * Verify the requested CN - only call this if cn is not NULL!
+ */
+static void x509_crt_verify_name( const mbedtls_x509_crt *crt,
+                                  const char *cn,
+                                  uint32_t *flags )
+{
+    const mbedtls_x509_name *name;
+    const mbedtls_x509_sequence *cur;
+    size_t cn_len = strlen( cn );
+
+    if( crt->ext_types & MBEDTLS_X509_EXT_SUBJECT_ALT_NAME )
+    {
+        for( cur = &crt->subject_alt_names; cur != NULL; cur = cur->next )
+        {
+            if( x509_crt_check_cn( &cur->buf, cn, cn_len ) == 0 )
+                break;
+        }
+
+        if( cur == NULL )
+            *flags |= MBEDTLS_X509_BADCERT_CN_MISMATCH;
+    }
+    else
+    {
+        for( name = &crt->subject; name != NULL; name = name->next )
+        {
+            if( MBEDTLS_OID_CMP( MBEDTLS_OID_AT_CN, &name->oid ) == 0 &&
+                x509_crt_check_cn( &name->val, cn, cn_len ) == 0 )
+            {
+                break;
+            }
+        }
+
+        if( name == NULL )
+            *flags |= MBEDTLS_X509_BADCERT_CN_MISMATCH;
+    }
+}
+
+/*
+ * Merge the flags for all certs in the chain, after calling callback
+ */
+static int x509_crt_merge_flags_with_cb(
+           uint32_t *flags,
+           const mbedtls_x509_crt_verify_chain *ver_chain,
+           int (*f_vrfy)(void *, mbedtls_x509_crt *, int, uint32_t *),
+           void *p_vrfy )
+{
+    int ret;
+    unsigned i;
+    uint32_t cur_flags;
+    const mbedtls_x509_crt_verify_chain_item *cur;
+
+    for( i = ver_chain->len; i != 0; --i )
+    {
+        cur = &ver_chain->items[i-1];
+        cur_flags = cur->flags;
+
+        if( NULL != f_vrfy )
+            if( ( ret = f_vrfy( p_vrfy, cur->crt, (int) i-1, &cur_flags ) ) != 0 )
+                return( ret );
+
+        *flags |= cur_flags;
+    }
+
+    return( 0 );
+}
+
+/*
+ * Verify the certificate validity (default profile, not restartable)
  */
 int mbedtls_x509_crt_verify( mbedtls_x509_crt *crt,
                      mbedtls_x509_crt *trust_ca,
@@ -2182,13 +2502,13 @@
                      int (*f_vrfy)(void *, mbedtls_x509_crt *, int, uint32_t *),
                      void *p_vrfy )
 {
-    return( mbedtls_x509_crt_verify_with_profile( crt, trust_ca, ca_crl,
-                &mbedtls_x509_crt_profile_default, cn, flags, f_vrfy, p_vrfy ) );
+    return( mbedtls_x509_crt_verify_restartable( crt, trust_ca, ca_crl,
+                &mbedtls_x509_crt_profile_default, cn, flags,
+                f_vrfy, p_vrfy, NULL ) );
 }
 
-
 /*
- * Verify the certificate validity, with profile
+ * Verify the certificate validity (user-chosen profile, not restartable)
  */
 int mbedtls_x509_crt_verify_with_profile( mbedtls_x509_crt *crt,
                      mbedtls_x509_crt *trust_ca,
@@ -2198,15 +2518,37 @@
                      int (*f_vrfy)(void *, mbedtls_x509_crt *, int, uint32_t *),
                      void *p_vrfy )
 {
-    size_t cn_len;
+    return( mbedtls_x509_crt_verify_restartable( crt, trust_ca, ca_crl,
+                profile, cn, flags, f_vrfy, p_vrfy, NULL ) );
+}
+
+/*
+ * Verify the certificate validity, with profile, restartable version
+ *
+ * This function:
+ *  - checks the requested CN (if any)
+ *  - checks the type and size of the EE cert's key,
+ *    as that isn't done as part of chain building/verification currently
+ *  - builds and verifies the chain
+ *  - then calls the callback and merges the flags
+ */
+int mbedtls_x509_crt_verify_restartable( mbedtls_x509_crt *crt,
+                     mbedtls_x509_crt *trust_ca,
+                     mbedtls_x509_crl *ca_crl,
+                     const mbedtls_x509_crt_profile *profile,
+                     const char *cn, uint32_t *flags,
+                     int (*f_vrfy)(void *, mbedtls_x509_crt *, int, uint32_t *),
+                     void *p_vrfy,
+                     mbedtls_x509_crt_restart_ctx *rs_ctx )
+{
     int ret;
-    int pathlen = 0, selfsigned = 0;
-    mbedtls_x509_crt *parent;
-    mbedtls_x509_name *name;
-    mbedtls_x509_sequence *cur = NULL;
     mbedtls_pk_type_t pk_type;
+    mbedtls_x509_crt_verify_chain ver_chain;
+    uint32_t ee_flags;
 
     *flags = 0;
+    ee_flags = 0;
+    x509_crt_verify_chain_reset( &ver_chain );
 
     if( profile == NULL )
     {
@@ -2214,106 +2556,38 @@
         goto exit;
     }
 
+    /* check name if requested */
     if( cn != NULL )
-    {
-        name = &crt->subject;
-        cn_len = strlen( cn );
-
-        if( crt->ext_types & MBEDTLS_X509_EXT_SUBJECT_ALT_NAME )
-        {
-            cur = &crt->subject_alt_names;
-
-            while( cur != NULL )
-            {
-                if( cur->buf.len == cn_len &&
-                    x509_memcasecmp( cn, cur->buf.p, cn_len ) == 0 )
-                    break;
-
-                if( cur->buf.len > 2 &&
-                    memcmp( cur->buf.p, "*.", 2 ) == 0 &&
-                    x509_check_wildcard( cn, &cur->buf ) == 0 )
-                {
-                    break;
-                }
-
-                cur = cur->next;
-            }
-
-            if( cur == NULL )
-                *flags |= MBEDTLS_X509_BADCERT_CN_MISMATCH;
-        }
-        else
-        {
-            while( name != NULL )
-            {
-                if( MBEDTLS_OID_CMP( MBEDTLS_OID_AT_CN, &name->oid ) == 0 )
-                {
-                    if( name->val.len == cn_len &&
-                        x509_memcasecmp( name->val.p, cn, cn_len ) == 0 )
-                        break;
-
-                    if( name->val.len > 2 &&
-                        memcmp( name->val.p, "*.", 2 ) == 0 &&
-                        x509_check_wildcard( cn, &name->val ) == 0 )
-                        break;
-                }
-
-                name = name->next;
-            }
-
-            if( name == NULL )
-                *flags |= MBEDTLS_X509_BADCERT_CN_MISMATCH;
-        }
-    }
+        x509_crt_verify_name( crt, cn, &ee_flags );
 
     /* Check the type and size of the key */
     pk_type = mbedtls_pk_get_type( &crt->pk );
 
     if( x509_profile_check_pk_alg( profile, pk_type ) != 0 )
-        *flags |= MBEDTLS_X509_BADCERT_BAD_PK;
+        ee_flags |= MBEDTLS_X509_BADCERT_BAD_PK;
 
-    if( x509_profile_check_key( profile, pk_type, &crt->pk ) != 0 )
-        *flags |= MBEDTLS_X509_BADCERT_BAD_KEY;
+    if( x509_profile_check_key( profile, &crt->pk ) != 0 )
+        ee_flags |= MBEDTLS_X509_BADCERT_BAD_KEY;
 
-    /* Look for a parent in trusted CAs */
-    for( parent = trust_ca; parent != NULL; parent = parent->next )
-    {
-        if( x509_crt_check_parent( crt, parent, 0, pathlen == 0 ) == 0 )
-            break;
-    }
+    /* Check the chain */
+    ret = x509_crt_verify_chain( crt, trust_ca, ca_crl, profile,
+                                 &ver_chain, rs_ctx );
 
-    if( parent != NULL )
-    {
-        ret = x509_crt_verify_top( crt, parent, ca_crl, profile,
-                                   pathlen, selfsigned, flags, f_vrfy, p_vrfy );
-        if( ret != 0 )
-            goto exit;
-    }
-    else
-    {
-        /* Look for a parent upwards the chain */
-        for( parent = crt->next; parent != NULL; parent = parent->next )
-            if( x509_crt_check_parent( crt, parent, 0, pathlen == 0 ) == 0 )
-                break;
+    if( ret != 0 )
+        goto exit;
 
-        /* Are we part of the chain or at the top? */
-        if( parent != NULL )
-        {
-            ret = x509_crt_verify_child( crt, parent, trust_ca, ca_crl, profile,
-                                         pathlen, selfsigned, flags, f_vrfy, p_vrfy );
-            if( ret != 0 )
-                goto exit;
-        }
-        else
-        {
-            ret = x509_crt_verify_top( crt, trust_ca, ca_crl, profile,
-                                       pathlen, selfsigned, flags, f_vrfy, p_vrfy );
-            if( ret != 0 )
-                goto exit;
-        }
-    }
+    /* Merge end-entity flags */
+    ver_chain.items[0].flags |= ee_flags;
+
+    /* Build final flags, calling callback on the way if any */
+    ret = x509_crt_merge_flags_with_cb( flags, &ver_chain, f_vrfy, p_vrfy );
 
 exit:
+#if defined(MBEDTLS_ECDSA_C) && defined(MBEDTLS_ECP_RESTARTABLE)
+    if( rs_ctx != NULL && ret != MBEDTLS_ERR_ECP_IN_PROGRESS )
+        mbedtls_x509_crt_restart_free( rs_ctx );
+#endif
+
     /* prevent misuse of the vrfy callback - VERIFY_FAILED would be ignored by
      * the SSL module for authmode optional, but non-zero return from the
      * callback means a fatal error so it shouldn't be ignored */
@@ -2368,7 +2642,7 @@
         {
             name_prv = name_cur;
             name_cur = name_cur->next;
-            mbedtls_zeroize( name_prv, sizeof( mbedtls_x509_name ) );
+            mbedtls_platform_zeroize( name_prv, sizeof( mbedtls_x509_name ) );
             mbedtls_free( name_prv );
         }
 
@@ -2377,7 +2651,7 @@
         {
             name_prv = name_cur;
             name_cur = name_cur->next;
-            mbedtls_zeroize( name_prv, sizeof( mbedtls_x509_name ) );
+            mbedtls_platform_zeroize( name_prv, sizeof( mbedtls_x509_name ) );
             mbedtls_free( name_prv );
         }
 
@@ -2386,7 +2660,8 @@
         {
             seq_prv = seq_cur;
             seq_cur = seq_cur->next;
-            mbedtls_zeroize( seq_prv, sizeof( mbedtls_x509_sequence ) );
+            mbedtls_platform_zeroize( seq_prv,
+                                      sizeof( mbedtls_x509_sequence ) );
             mbedtls_free( seq_prv );
         }
 
@@ -2395,13 +2670,14 @@
         {
             seq_prv = seq_cur;
             seq_cur = seq_cur->next;
-            mbedtls_zeroize( seq_prv, sizeof( mbedtls_x509_sequence ) );
+            mbedtls_platform_zeroize( seq_prv,
+                                      sizeof( mbedtls_x509_sequence ) );
             mbedtls_free( seq_prv );
         }
 
         if( cert_cur->raw.p != NULL )
         {
-            mbedtls_zeroize( cert_cur->raw.p, cert_cur->raw.len );
+            mbedtls_platform_zeroize( cert_cur->raw.p, cert_cur->raw.len );
             mbedtls_free( cert_cur->raw.p );
         }
 
@@ -2415,11 +2691,43 @@
         cert_prv = cert_cur;
         cert_cur = cert_cur->next;
 
-        mbedtls_zeroize( cert_prv, sizeof( mbedtls_x509_crt ) );
+        mbedtls_platform_zeroize( cert_prv, sizeof( mbedtls_x509_crt ) );
         if( cert_prv != crt )
             mbedtls_free( cert_prv );
     }
     while( cert_cur != NULL );
 }
 
+#if defined(MBEDTLS_ECDSA_C) && defined(MBEDTLS_ECP_RESTARTABLE)
+/*
+ * Initialize a restart context
+ */
+void mbedtls_x509_crt_restart_init( mbedtls_x509_crt_restart_ctx *ctx )
+{
+    mbedtls_pk_restart_init( &ctx->pk );
+
+    ctx->parent = NULL;
+    ctx->fallback_parent = NULL;
+    ctx->fallback_signature_is_good = 0;
+
+    ctx->parent_is_trusted = -1;
+
+    ctx->in_progress = x509_crt_rs_none;
+    ctx->self_cnt = 0;
+    x509_crt_verify_chain_reset( &ctx->ver_chain );
+}
+
+/*
+ * Free the components of a restart context
+ */
+void mbedtls_x509_crt_restart_free( mbedtls_x509_crt_restart_ctx *ctx )
+{
+    if( ctx == NULL )
+        return;
+
+    mbedtls_pk_restart_free( &ctx->pk );
+    mbedtls_x509_crt_restart_init( ctx );
+}
+#endif /* MBEDTLS_ECDSA_C && MBEDTLS_ECP_RESTARTABLE */
+
 #endif /* MBEDTLS_X509_CRT_PARSE_C */