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SHA-1 deprecation: allow it in key exchange

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By default, keep allowing SHA-1 in key exchange signatures. Disabling
it causes compatibility issues, especially with clients that use
TLS1.2 but don't send the signature_algorithms extension.

SHA-1 is forbidden in certificates by default, since it's vulnerable
to offline collision-based attacks.
This commit is contained in:
Gilles Peskine 2017-05-12 13:16:40 +02:00 • committed by Manuel Pégourié-Gonnard
parent 682df09159
commit 5d2511c4d4
7 changed files with 32 additions and 17 deletions
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23
include/mbedtls/config.h
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@ -2638,13 +2638,24 @@
//#define MBEDTLS_X509_MAX_FILE_PATH_LEN 512 /**< Maximum length of a path/filename string in bytes including the null terminator character ('\0'). */
/**
* Allow SHA-1 in the default TLS configuration for certificate signing and
* TLS 1.2 handshake signature. Without this build-time option, SHA-1
* support must be activated explicitly through mbedtls_ssl_conf_cert_profile
* and mbedtls_ssl_conf_sig_hashes. The use of SHA-1 in TLS <= 1.1 and in
* HMAC-SHA-1 for XXX_SHA ciphersuites is always allowed by default.
* Allow SHA-1 in the default TLS configuration for certificate signing.
* Without this build-time option, SHA-1 support must be activated explicitly
* through mbedtls_ssl_conf_cert_profile. Turning on this option is not
* recommended because of it is possible to generte SHA-1 collisions, however
* this may be safe for legacy infrastructure where additional controls apply.
*/
// #define MBEDTLS_TLS_DEFAULT_ALLOW_SHA1
// #define MBEDTLS_TLS_DEFAULT_ALLOW_SHA1_IN_CERTIFICATES
/**
* Allow SHA-1 in the default TLS configuration for TLS 1.2 handshake
* signature and ciphersuite selection. Without this build-time option, SHA-1
* support must be activated explicitly through mbedtls_ssl_conf_sig_hashes.
* The use of SHA-1 in TLS <= 1.1 and in HMAC-SHA-1 is always allowed by
* default. At the time of writing, there is no practical attack on the use
* of SHA-1 in handshake signatures, hence this option is turned on by default
* for compatibility with existing peers.
*/
#define MBEDTLS_TLS_DEFAULT_ALLOW_SHA1_IN_KEY_EXCHANGE
/* \} name SECTION: Customisation configuration options */