Fix rsaz 512 overflow bug [1.0.2] #10576
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There is an overflow bug in the x64_64 Montgomery squaring procedure used in exponentiation with 512-bit moduli. No EC algorithms are affected. Analysis suggests that attacks against 2-prime RSA1024, 3-prime RSA1536, and DSA1024 as a result of this defect would be very difficult to perform and are not believed likely. Attacks against DH512 are considered just feasible. However, for an attack the target would have to re-use the DH512 private key, which is not recommended anyway. Also applications directly using the low level API BN_mod_exp may be affected if they use BN_FLG_CONSTTIME. CVE-2019-1551
We have always a carry in %rcx or %rbx in range 0..2 from the previous stage, that is added to the result of the 64-bit square, but the low nibble of any square can only be 0, 1, 4, 9. Therefore one "adcq $0, %rdx" can be removed. Likewise in the ADX code we can remove one "adcx %rbp, $out" since %rbp is always 0, and carry is also zero, therefore that is a no-op.
This was referenced Dec 4, 2019
openssl-machine
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There is an overflow bug in the x64_64 Montgomery squaring procedure used in exponentiation with 512-bit moduli. No EC algorithms are affected. Analysis suggests that attacks against 2-prime RSA1024, 3-prime RSA1536, and DSA1024 as a result of this defect would be very difficult to perform and are not believed likely. Attacks against DH512 are considered just feasible. However, for an attack the target would have to re-use the DH512 private key, which is not recommended anyway. Also applications directly using the low level API BN_mod_exp may be affected if they use BN_FLG_CONSTTIME. CVE-2019-1551 Reviewed-by: Paul Dale <paul.dale@oracle.com> Reviewed-by: Bernd Edlinger <bernd.edlinger@hotmail.de> (Merged from #10576)
openssl-machine
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Dec 6, 2019
We have always a carry in %rcx or %rbx in range 0..2 from the previous stage, that is added to the result of the 64-bit square, but the low nibble of any square can only be 0, 1, 4, 9. Therefore one "adcq $0, %rdx" can be removed. Likewise in the ADX code we can remove one "adcx %rbp, $out" since %rbp is always 0, and carry is also zero, therefore that is a no-op. Reviewed-by: Paul Dale <paul.dale@oracle.com> (Merged from #10576)
openssl-machine
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Reviewed-by: Paul Dale <paul.dale@oracle.com> (Merged from #10576)
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Merged to 1.0.2, thanks! |
tetatetit
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There is an overflow bug in the x64_64 Montgomery squaring procedure used in exponentiation with 512-bit moduli. No EC algorithms are affected. Analysis suggests that attacks against 2-prime RSA1024, 3-prime RSA1536, and DSA1024 as a result of this defect would be very difficult to perform and are not believed likely. Attacks against DH512 are considered just feasible. However, for an attack the target would have to re-use the DH512 private key, which is not recommended anyway. Also applications directly using the low level API BN_mod_exp may be affected if they use BN_FLG_CONSTTIME. CVE-2019-1551 Reviewed-by: Paul Dale <paul.dale@oracle.com> Reviewed-by: Bernd Edlinger <bernd.edlinger@hotmail.de> (Merged from openssl#10576)
tetatetit
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Dec 20, 2019
We have always a carry in %rcx or %rbx in range 0..2 from the previous stage, that is added to the result of the 64-bit square, but the low nibble of any square can only be 0, 1, 4, 9. Therefore one "adcq $0, %rdx" can be removed. Likewise in the ADX code we can remove one "adcx %rbp, $out" since %rbp is always 0, and carry is also zero, therefore that is a no-op. Reviewed-by: Paul Dale <paul.dale@oracle.com> (Merged from openssl#10576)
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Fix for CVE-2019-1551, 1.0.2 branch, (white space only merge conflicts in the assembler part)
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