Implement TLS 1.3 key evolution function
Signed-off-by: Hanno Becker <hanno.becker@arm.com>
diff --git a/library/ssl_tls13_keys.c b/library/ssl_tls13_keys.c
index d9d5d98..1d61455 100644
--- a/library/ssl_tls13_keys.c
+++ b/library/ssl_tls13_keys.c
@@ -285,4 +285,66 @@
dstbuf, buflen ) );
}
+int mbedtls_ssl_tls1_3_evolve_secret(
+ mbedtls_md_type_t hash_alg,
+ const unsigned char *secret_old,
+ const unsigned char *input, size_t input_len,
+ unsigned char *secret_new )
+{
+ int ret = MBEDTLS_ERR_SSL_INTERNAL_ERROR;
+ size_t hlen, ilen;
+ unsigned char _secret[ MBEDTLS_MD_MAX_SIZE ] = { 0 };
+ unsigned char _input [ MBEDTLS_MD_MAX_SIZE ] = { 0 };
+
+ const mbedtls_md_info_t *md;
+ md = mbedtls_md_info_from_type( hash_alg );
+ if( md == NULL )
+ return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
+
+ hlen = mbedtls_md_get_size( md );
+
+ /* For non-initial runs, call Derive-Secret( ., "derived", "")
+ * on the old secreet. */
+ if( secret_old != NULL )
+ {
+ ret = mbedtls_ssl_tls1_3_derive_secret(
+ hash_alg,
+ secret_old, hlen,
+ MBEDTLS_SSL_TLS1_3_LBL_WITH_LEN( derived ),
+ NULL, 0, /* context */
+ MBEDTLS_SSL_TLS1_3_CONTEXT_UNHASHED,
+ _secret, hlen );
+ if( ret != 0 )
+ goto cleanup;
+ }
+
+ if( input != NULL )
+ {
+ memcpy( _input, input, input_len );
+ ilen = input_len;
+ }
+ else
+ {
+ ilen = hlen;
+ }
+
+ /* HKDF-Extract takes a salt and input key material.
+ * The salt is the old secret, and the input key material
+ * is the input secret (PSK / ECDHE). */
+ ret = mbedtls_hkdf_extract( md,
+ _secret, hlen,
+ _input, ilen,
+ secret_new );
+ if( ret != 0 )
+ goto cleanup;
+
+ ret = 0;
+
+ cleanup:
+
+ mbedtls_platform_zeroize( _secret, sizeof(_secret) );
+ mbedtls_platform_zeroize( _input, sizeof(_input) );
+ return( ret );
+}
+
#endif /* MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL */
