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Zeroize local AES variables before exiting the function

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This issue has been reported by Tuba Yavuz, Farhaan Fowze, Ken (Yihang) Bai,
Grant Hernandez, and Kevin Butler (University of Florida) and
Dave Tian (Purdue University).

In AES encrypt and decrypt some variables were left on the stack. The value
of these variables can be used to recover the last round key. To follow best
practice and to limit the impact of buffer overread vulnerabilities (like
Heartbleed) we need to zeroize them before exiting the function.
This commit is contained in:
Andrzej Kurek 2019-11-12 03:34:03 -05:00 committed by Simon Butcher
parent e9db2aa5b4
commit a8405447aa
2 changed files with 32 additions and 0 deletions
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8
ChangeLog
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@ -71,6 +71,14 @@ Security
blinded value, factor it (as it is smaller than RSA keys and not guaranteed
to have only large prime factors), and then, by brute force, recover the
key. Reported by Alejandro Cabrera Aldaya and Billy Brumley.
* Zeroize local variables in mbedtls_internal_aes_encrypt() and
mbedtls_internal_aes_decrypt() before exiting the function. The value of
these variables can be used to recover the last round key. To follow best
practice and to limit the impact of buffer overread vulnerabilities (like
Heartbleed) we need to zeroize them before exiting the function.
Issue reported by Tuba Yavuz, Farhaan Fowze, Ken (Yihang) Bai,
Grant Hernandez, and Kevin Butler (University of Florida) and
Dave Tian (Purdue University).
Bugfix
* Remove redundant line for getting the bitlen of a bignum, since the variable

24
library/aes.c
View File

@ -1246,6 +1246,18 @@ int mbedtls_internal_aes_encrypt( mbedtls_aes_context *ctx,
PUT_UINT32_LE( X2, output, 8 );
PUT_UINT32_LE( X3, output, 12 );
mbedtls_platform_zeroize( &X0, sizeof( X0 ) );
mbedtls_platform_zeroize( &X1, sizeof( X1 ) );
mbedtls_platform_zeroize( &X2, sizeof( X2 ) );
mbedtls_platform_zeroize( &X3, sizeof( X3 ) );
mbedtls_platform_zeroize( &Y0, sizeof( Y0 ) );
mbedtls_platform_zeroize( &Y1, sizeof( Y1 ) );
mbedtls_platform_zeroize( &Y2, sizeof( Y2 ) );
mbedtls_platform_zeroize( &Y3, sizeof( Y3 ) );
mbedtls_platform_zeroize( &RK, sizeof( RK ) );
return( 0 );
}
#endif /* MBEDTLS_AES_SCA_COUNTERMEASURES */
@ -1513,6 +1525,18 @@ int mbedtls_internal_aes_decrypt( mbedtls_aes_context *ctx,
PUT_UINT32_LE( X2, output, 8 );
PUT_UINT32_LE( X3, output, 12 );
mbedtls_platform_zeroize( &X0, sizeof( X0 ) );
mbedtls_platform_zeroize( &X1, sizeof( X1 ) );
mbedtls_platform_zeroize( &X2, sizeof( X2 ) );
mbedtls_platform_zeroize( &X3, sizeof( X3 ) );
mbedtls_platform_zeroize( &Y0, sizeof( Y0 ) );
mbedtls_platform_zeroize( &Y1, sizeof( Y1 ) );
mbedtls_platform_zeroize( &Y2, sizeof( Y2 ) );
mbedtls_platform_zeroize( &Y3, sizeof( Y3 ) );
mbedtls_platform_zeroize( &RK, sizeof( RK ) );
return( 0 );
}
#endif /* MBEDTLS_AES_SCA_COUNTERMEASURES */