Use in-place decryption in pk_parse_pkcs8_encrypted_der
The stack buffer used to hold the decrypted key in pk_parse_pkcs8_encrypted_der
was statically sized to 2048 bytes, which is not enough for DER encoded 4096bit
RSA keys.
This commit resolves the problem by performing the key-decryption in-place,
circumventing the introduction of another stack or heap copy of the key.
There are two situations where pk_parse_pkcs8_encrypted_der is invoked:
1. When processing a PEM-encoded encrypted key in mbedtls_pk_parse_key.
This does not need adaption since the PEM context used to hold the decoded
key is already constructed and owned by mbedtls_pk_parse_key.
2. When processing a DER-encoded encrypted key in mbedtls_pk_parse_key.
In this case, mbedtls_pk_parse_key calls pk_parse_pkcs8_encrypted_der with
the buffer provided by the user, which is declared const. The commit
therefore adds a small code paths making a copy of the keybuffer before
calling pk_parse_pkcs8_encrypted_der.
diff --git a/library/pkparse.c b/library/pkparse.c
index de0881a..3368f5b 100644
--- a/library/pkparse.c
+++ b/library/pkparse.c
@@ -936,12 +936,12 @@
#if defined(MBEDTLS_PKCS12_C) || defined(MBEDTLS_PKCS5_C)
static int pk_parse_key_pkcs8_encrypted_der(
mbedtls_pk_context *pk,
- const unsigned char *key, size_t keylen,
+ unsigned char *key, size_t keylen,
const unsigned char *pwd, size_t pwdlen )
{
int ret, decrypted = 0;
size_t len;
- unsigned char buf[2048];
+ unsigned char *buf;
unsigned char *p, *end;
mbedtls_asn1_buf pbe_alg_oid, pbe_params;
#if defined(MBEDTLS_PKCS12_C)
@@ -949,8 +949,6 @@
mbedtls_md_type_t md_alg;
#endif
- memset( buf, 0, sizeof( buf ) );
-
p = (unsigned char *) key;
end = p + keylen;
@@ -985,8 +983,7 @@
if( ( ret = mbedtls_asn1_get_tag( &p, end, &len, MBEDTLS_ASN1_OCTET_STRING ) ) != 0 )
return( MBEDTLS_ERR_PK_KEY_INVALID_FORMAT + ret );
- if( len > sizeof( buf ) )
- return( MBEDTLS_ERR_PK_BAD_INPUT_DATA );
+ buf = p;
/*
* Decrypt EncryptedData with appropriate PDE
@@ -1087,7 +1084,7 @@
return( MBEDTLS_ERR_PK_UNKNOWN_PK_ALG );
}
- if( ( ret = mbedtls_pk_setup( pk, pk_info ) ) != 0 ||
+ if( ( ret = mbedtls_pk_setup( pk, pk_info ) ) != 0 ||
( ret = pk_parse_key_pkcs1_der( mbedtls_pk_rsa( *pk ),
pem.buf, pem.buflen ) ) != 0 )
{
@@ -1122,7 +1119,7 @@
return( MBEDTLS_ERR_PK_UNKNOWN_PK_ALG );
}
- if( ( ret = mbedtls_pk_setup( pk, pk_info ) ) != 0 ||
+ if( ( ret = mbedtls_pk_setup( pk, pk_info ) ) != 0 ||
( ret = pk_parse_key_sec1_der( mbedtls_pk_ec( *pk ),
pem.buf, pem.buflen ) ) != 0 )
{
@@ -1200,12 +1197,24 @@
* error
*/
#if defined(MBEDTLS_PKCS12_C) || defined(MBEDTLS_PKCS5_C)
- if( ( ret = pk_parse_key_pkcs8_encrypted_der( pk, key, keylen,
- pwd, pwdlen ) ) == 0 )
{
- return( 0 );
+ unsigned char *key_copy;
+
+ if( ( key_copy = mbedtls_calloc( 1, keylen ) ) == NULL )
+ return( MBEDTLS_ERR_PK_ALLOC_FAILED );
+
+ memcpy( key_copy, key, keylen );
+
+ ret = pk_parse_key_pkcs8_encrypted_der( pk, key_copy, keylen,
+ pwd, pwdlen );
+
+ mbedtls_zeroize( key_copy, keylen );
+ mbedtls_free( key_copy );
}
+ if( ret == 0 )
+ return( 0 );
+
mbedtls_pk_free( pk );
if( ret == MBEDTLS_ERR_PK_PASSWORD_MISMATCH )
@@ -1223,7 +1232,7 @@
if( ( pk_info = mbedtls_pk_info_from_type( MBEDTLS_PK_RSA ) ) == NULL )
return( MBEDTLS_ERR_PK_UNKNOWN_PK_ALG );
- if( ( ret = mbedtls_pk_setup( pk, pk_info ) ) != 0 ||
+ if( ( ret = mbedtls_pk_setup( pk, pk_info ) ) != 0 ||
( ret = pk_parse_key_pkcs1_der( mbedtls_pk_rsa( *pk ), key, keylen ) ) == 0 )
{
return( 0 );
@@ -1236,7 +1245,7 @@
if( ( pk_info = mbedtls_pk_info_from_type( MBEDTLS_PK_ECKEY ) ) == NULL )
return( MBEDTLS_ERR_PK_UNKNOWN_PK_ALG );
- if( ( ret = mbedtls_pk_setup( pk, pk_info ) ) != 0 ||
+ if( ( ret = mbedtls_pk_setup( pk, pk_info ) ) != 0 ||
( ret = pk_parse_key_sec1_der( mbedtls_pk_ec( *pk ), key, keylen ) ) == 0 )
{
return( 0 );