From b2be1fca2c2e61abd155f557b18b5a3dfb6cf707 Mon Sep 17 00:00:00 2001 From: Gilles Peskine Date: Thu, 28 Nov 2019 09:45:32 +0100 Subject: [PATCH] Catch AES failure in mbedtls_ctr_drbg_random The functions mbedtls_ctr_drbg_random() and mbedtls_ctr_drbg_random_with_add() could return 0 if an AES function failed. This could only happen with alternative AES implementations (the built-in implementation of the AES functions involved never fail), typically due to a failure in a hardware accelerator. Bug reported and fix proposed by Johan Uppman Bruce and Christoffer Lauri, Sectra. --- ChangeLog | 4 ++++ library/ctr_drbg.c | 2 +- 2 files changed, 5 insertions(+), 1 deletion(-) diff --git a/ChangeLog b/ChangeLog index c9583015d..0de4fa0f8 100644 --- a/ChangeLog +++ b/ChangeLog @@ -20,6 +20,10 @@ Security timings on the comparison in the key generation enabled the attacker to learn leading bits of the ephemeral key used during ECDSA signatures and to recover the private key. + * Catch failure of AES functions in mbedtls_ctr_drbg_random(). Uncaught + failures could happen with alternative implementations of AES. Bug + reported and fix proposed by Johan Uppman Bruce and Christoffer Lauri, + Sectra. Changes * Add unit tests for AES-GCM when called through mbedtls_cipher_auth_xxx() diff --git a/library/ctr_drbg.c b/library/ctr_drbg.c index d7a94840c..726e58af8 100644 --- a/library/ctr_drbg.c +++ b/library/ctr_drbg.c @@ -457,7 +457,7 @@ int mbedtls_ctr_drbg_random_with_add( void *p_rng, exit: mbedtls_zeroize( add_input, sizeof( add_input ) ); mbedtls_zeroize( tmp, sizeof( tmp ) ); - return( 0 ); + return( ret ); } int mbedtls_ctr_drbg_random( void *p_rng, unsigned char *output, size_t output_len )