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Catch AES failure in mbedtls_ctr_drbg_random

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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.
This commit is contained in:
Gilles Peskine 2019-11-28 09:45:32 +01:00 committed by Simon Butcher
parent bcdd8bcfcf
commit 8b7f03f172
2 changed files with 9 additions and 1 deletions
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8
ChangeLog
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@ -79,6 +79,14 @@ Security
Issue reported by Tuba Yavuz, Farhaan Fowze, Ken (Yihang) Bai,
Grant Hernandez, and Kevin Butler (University of Florida) and
Dave Tian (Purdue University).
* Fix side channel vulnerability in ECDSA key generation. Obtaining precise
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. Reported by Jeremy Dubeuf.
* 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.
Bugfix
* Remove redundant line for getting the bitlen of a bignum, since the variable

2
library/ctr_drbg.c
View File

@ -512,7 +512,7 @@ int mbedtls_ctr_drbg_random_with_add( void *p_rng,
exit:
mbedtls_platform_zeroize( add_input, sizeof( add_input ) );
mbedtls_platform_zeroize( tmp, sizeof( tmp ) );
return( 0 );
return( ret );
}
int mbedtls_ctr_drbg_random( void *p_rng, unsigned char *output, size_t output_len )