commit 955738a4f254073b5ceb9b64dcf2d8465703889d
author Gilles Peskine <Gilles.Peskine@arm.com> Thu May 04 16:17:21 2017 +0200
committer Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com> Tue Jun 06 19:08:19 2017 +0200
tree 41f96857bcdfaa2cc8ae35b97079a5b0fe58c078
parent cd6e4d5bccf939318cea4c639361ef634c96722f

Remove SHA-1 in TLS by default

Default to forbidding the use of SHA-1 in TLS where it is unsafe: for
certificate signing, and as the signature hash algorithm for the TLS
1.2 handshake signature. SHA-1 remains allowed in HMAC-SHA-1 in the
XXX_SHA ciphersuites and in the PRF for TLS <= 1.1.

For easy backward compatibility for use in controlled environments,
turn on the MBEDTLS_TLS_DEFAULT_ALLOW_SHA1 compiled-time option.

library/ssl_tls.c

diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 4023854..f2f08c7 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -7043,7 +7043,7 @@
     MBEDTLS_MD_SHA256,
     MBEDTLS_MD_SHA224,
 #endif
-#if defined(MBEDTLS_SHA1_C)
+#if defined(MBEDTLS_SHA1_C) && defined(MBEDTLS_TLS_DEFAULT_ALLOW_SHA1)
     MBEDTLS_MD_SHA1,
 #endif
     MBEDTLS_MD_NONE

library/x509_crt.c

diff --git a/library/x509_crt.c b/library/x509_crt.c
index 84a2d4f..ca3a7d0 100644
--- a/library/x509_crt.c
+++ b/library/x509_crt.c
@@ -85,9 +85,11 @@
  */
 const mbedtls_x509_crt_profile mbedtls_x509_crt_profile_default =
 {
-    /* Hashes from SHA-1 and above */
+#if defined(MBEDTLS_TLS_DEFAULT_ALLOW_SHA1)
+    /* Allow SHA-1 (weak, but still safe in controlled environments) */
     MBEDTLS_X509_ID_FLAG( MBEDTLS_MD_SHA1 ) |
-    MBEDTLS_X509_ID_FLAG( MBEDTLS_MD_RIPEMD160 ) |
+#endif
+    /* Only SHA-2 hashes */
     MBEDTLS_X509_ID_FLAG( MBEDTLS_MD_SHA224 ) |
     MBEDTLS_X509_ID_FLAG( MBEDTLS_MD_SHA256 ) |
     MBEDTLS_X509_ID_FLAG( MBEDTLS_MD_SHA384 ) |