On Monday, August 18, 2014 2:34:30 PM UTC-4, [email protected] wrote:
>
> Hello. I have a question. When signing something using DSA or ECDSA, is
> there a way to override the k-value supplied by Crypto++? I've been looking
> into the code and haven't been able to find a definitive answer just yet.
> Any help would be greatly appreciated.
>
In the case of DSA, the signing occurs in gfpcrypt.h:
00152 class DL_Algorithm_GDSA : public DL_ElgamalLikeSignatureAlgorithm<T>
00153 {
00154 public:
00155 static const char * CRYPTOPP_API StaticAlgorithmName()
{return "DSA-1363";}
00156
00157 void Sign(const DL_GroupParameters<T> ¶ms, const Integer
&x, const Integer &k, const Integer &e, Integer &r, Integer &s) const
00158 {
00159 const Integer &q = params.GetSubgroupOrder();
00160 r %= q;
00161 Integer kInv = k.InverseMod(q);
00162 s = (kInv * (x*r + e)) % q;
00163 assert(!!r && !!s);
00164 }
...
You might try working up from there. I suspect you'll encounter DL_Keys_DSA
on the way up. In particular:
00384 struct CRYPTOPP_DLL DSA : public DL_SS<
00385 DL_Keys_DSA,
00386 DL_Algorithm_GDSA<Integer>,
00387 DL_SignatureMessageEncodingMethod_DSA,
00388 SHA,
00389 DSA>
00390 {
...
That's probably where I would look to start adding a public method to set k
from the outside world.
Related:
* http://www.cryptopp.com/docs/ref/struct_d_l___keys___d_s_a.html
* http://www.cryptopp.com/docs/ref/gfpcrypt_8h_source.html
Jeff
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