public static byte[] SignRaw(ECPrivateKey sk, IDigest rfc6979Hash,
byte[] hash, int hashOff, int hashLen)
{
ECCurve curve = sk.Curve;
byte[] q = curve.SubgroupOrder;
RFC6979 rf = new RFC6979(rfc6979Hash, q, sk.X,
hash, hashOff, hashLen, rfc6979Hash != null);
ModInt mh = rf.GetHashMod();
ModInt mx = mh.Dup();
mx.Decode(sk.X);
/*
* Compute DSA signature. We use a loop to enumerate
* candidates for k until a proper one is found (it
* is VERY improbable that we may have to loop).
*/
ModInt mr = mh.Dup();
ModInt ms = mh.Dup();
ModInt mk = mh.Dup();
byte[] k = new byte[q.Length];
for (;;)
{
rf.NextK(k);
MutableECPoint G = curve.MakeGenerator();
if (G.MulSpecCT(k) == 0)
{
/*
* We may get an error here only if the
* curve is invalid (generator does not
* produce the expected subgroup).
*/
throw new CryptoException(
"Invalid EC private key / curve");
}
mr.DecodeReduce(G.X);
if (mr.IsZero)
{
continue;
}
ms.Set(mx);
ms.ToMonty();
ms.MontyMul(mr);
ms.Add(mh);
mk.Decode(k);
mk.Invert();
ms.ToMonty();
ms.MontyMul(mk);
byte[] sig = new byte[q.Length << 1];
mr.Encode(sig, 0, q.Length);
ms.Encode(sig, q.Length, q.Length);
return(sig);
}
}
public static bool VerifyRaw(ECPublicKey pk,
byte[] hash, int hashOff, int hashLen,
byte[] sig, int sigOff, int sigLen)
{
try {
/*
* Get the curve.
*/
ECCurve curve = pk.Curve;
/*
* Get r and s from signature. This also verifies
* that they do not exceed the subgroup order.
*/
if (sigLen == 0 || (sigLen & 1) != 0)
{
return(false);
}
int tlen = sigLen >> 1;
ModInt oneQ = new ModInt(curve.SubgroupOrder);
oneQ.Set(1);
ModInt r = oneQ.Dup();
ModInt s = oneQ.Dup();
r.Decode(sig, sigOff, tlen);
s.Decode(sig, sigOff + tlen, tlen);
/*
* If either r or s was too large, it got set to
* zero. We also don't want real zeros.
*/
if (r.IsZero || s.IsZero)
{
return(false);
}
/*
* Convert the hash value to an integer modulo q.
* As per FIPS 186-4, if the hash value is larger
* than q, then we keep the qlen leftmost bits of
* the hash value.
*/
int qBitLength = oneQ.ModBitLength;
int hBitLength = hashLen << 3;
byte[] hv;
if (hBitLength <= qBitLength)
{
hv = new byte[hashLen];
Array.Copy(hash, hashOff, hv, 0, hashLen);
}
else
{
int qlen = (qBitLength + 7) >> 3;
hv = new byte[qlen];
Array.Copy(hash, hashOff, hv, 0, qlen);
int rs = (8 - (qBitLength & 7)) & 7;
BigInt.RShift(hv, rs);
}
ModInt z = oneQ.Dup();
z.DecodeReduce(hv);
/*
* Apply the verification algorithm:
* w = 1/s mod q
* u = z*w mod q
* v = r*w mod q
* T = u*G + v*Pub
* test whether T.x mod q == r.
*/
/*
* w = 1/s mod q
*/
ModInt w = s.Dup();
w.Invert();
/*
* u = z*w mod q
*/
w.ToMonty();
ModInt u = w.Dup();
u.MontyMul(z);
/*
* v = r*w mod q
*/
ModInt v = w.Dup();
v.MontyMul(r);
/*
* Compute u*G
*/
MutableECPoint T = curve.MakeGenerator();
uint good = T.MulSpecCT(u.Encode());
/*
* Compute v*iPub
*/
MutableECPoint M = pk.iPub.Dup();
good &= M.MulSpecCT(v.Encode());
/*
* Compute T = u*G+v*iPub
*/
uint nd = T.AddCT(M);
M.DoubleCT();
T.Set(M, ~nd);
good &= ~T.IsInfinityCT;
/*
* Get T.x, reduced modulo q.
* Signature is valid if and only if we get
* the same value as r (and we did not encounter
* an error previously).
*/
s.DecodeReduce(T.X);
return((good & r.EqCT(s)) != 0);
} catch (CryptoException) {
/*
* Exceptions may occur if the key or signature
* have invalid values (non invertible, out of
* range...). Any such occurrence means that the
* signature is not valid.
*/
return(false);
}
}
