// Computes Kc as described in rfc 8554
public BitString Algorithm4b(BitString sig, BitString msg, BitString pubType, BitString I, BitString q)
{
// 1. If the signature is not at least four bytes long, return INVALID.
if (sig.BitLength < 32)
{
return(null);
}
// 2. Parse sigtype, C, and y from the signature as follows:
// a. sigtype = strTou32(first 4 bytes of signature)
var sigType = sig.MSBSubstring(0, 32);
// b. If sigtype is not equal to pubtype, return INVALID.
if (!pubType.Equals(sigType))
{
return(null);
}
// c. Set n and p according to the pubtype and Table 1; if the signature is not exactly 4 + n * (p + 1)
// bytes long, return INVALID.
var p = LmotsModeMapping.GetPFromCode(sigType);
var n = LmotsModeMapping.GetNFromCode(sigType);
if (sig.BitLength != (4 + (n * (p + 1))) * 8)
{
return(null);
}
// d. C = next n bytes of signature
var C = sig.MSBSubstring(32, n * 8);
// e. y[0] = next n bytes of signature
// y[1] = next n bytes of signature
// ...
// y[p - 1] = next n bytes of signature
var y = sig.MSBSubstring((n * 8) + 32, p * n * 8);
// 3. Compute the string Kc as described in rfc 8554
var Q = _sha256.HashMessage(I
.ConcatenateBits(q)
.ConcatenateBits(D_MESG)
.ConcatenateBits(C)
.ConcatenateBits(msg)).Digest;
var cksmQ = CheckSum(Q);
var QcksmQ = Q.ConcatenateBits(cksmQ);
var z = LmsDllLoader.GenZ(_p, _n, _w, y.ToBytes(), QcksmQ.ToBytes(), I.ToBytes(), q.ToBytes());
var concatenated = I.ConcatenateBits(q).ConcatenateBits(D_PBLC);
concatenated = concatenated.ConcatenateBits(new BitString(z));
var Kc = _sha256.HashMessage(concatenated).Digest;
// 4. Return Kc.
return(Kc);
}
public HssVerificationResult VerifyHssSignature(BitString msg, BitString publicKey, BitString signature)
{
// 1. The signature S is parsed into its components as follows:
// a. Nspk = strTou32(first four bytes of S)
// if Nspk+1 is not equal to the number of levels L in pub return INVALID
var Nspk = (int)signature.MSBSubstring(0, 32).ToPositiveBigInteger();
var lengthInPublic = (int)publicKey.MSBSubstring(0, 32).ToPositiveBigInteger();
if (Nspk + 1 != lengthInPublic)
{
return(new HssVerificationResult("Validation failed. L values do not match."));
}
// b. for (i = 0; i<Nspk; i = i + 1) {
// siglist[i] = next LMS signature parsed from S
// publist[i] = next LMS public key parsed from S
// }
var siglist = new BitString[Nspk + 1];
var publist = new BitString[Nspk + 1];
var currIndex = 32;
for (int i = 0; i < Nspk; i++)
{
// assume sig and pub have same LMS mode
var otsCode = signature.MSBSubstring(currIndex + 32, 32);
var n = LmotsModeMapping.GetNFromCode(otsCode);
var p = LmotsModeMapping.GetPFromCode(otsCode);
var sigtype = signature.MSBSubstring((8 + n * (p + 1)) * 8 + currIndex, 32);
var m = LmsModeMapping.GetMFromCode(sigtype);
var h = LmsModeMapping.GetHFromCode(sigtype);
var siglen = (12 + n * (p + 1) + m * h) * 8;
var publen = 192 + (m * 8);
siglist[i] = signature.MSBSubstring(currIndex, siglen);
currIndex += siglen;
publist[i] = signature.MSBSubstring(currIndex, publen);
currIndex += publen;
}
// c. siglist[Nspk] = next LMS signature parsed from S
var otsCodeLast = signature.MSBSubstring(currIndex + 32, 32);
var nLast = LmotsModeMapping.GetNFromCode(otsCodeLast);
var pLast = LmotsModeMapping.GetPFromCode(otsCodeLast);
var sigtypeLast = signature.MSBSubstring((8 + nLast * (pLast + 1)) * 8 + currIndex, 32);
var mLast = LmsModeMapping.GetMFromCode(sigtypeLast);
var hLast = LmsModeMapping.GetHFromCode(sigtypeLast);
var siglenLast = (12 + nLast * (pLast + 1) + mLast * hLast) * 8;
siglist[Nspk] = signature.MSBSubstring(currIndex, siglenLast);
// 2. Verify each part of the signature
var key = publicKey.MSBSubstring(32, publicKey.BitLength - 32);
for (int i = 0; i < Nspk; i++)
{
var result = _lms[i].VerifyLmsSignature(publist[i], key, siglist[i]);
if (!result.Success)
{
return(new HssVerificationResult("LMS Validation failed: " + result.ErrorMessage));
}
key = publist[i];
}
// 3. return lms_verify(message, key, siglist[Nspk])
var finalResult = _lms[Nspk].VerifyLmsSignature(msg, key, siglist[Nspk]);
if (finalResult.Success)
{
return(new HssVerificationResult());
}
else
{
return(new HssVerificationResult("Validation failed. Final check failed: " + finalResult.ErrorMessage));
}
}
public LmsVerificationResult VerifyLmsSignature(BitString msg, BitString publicKey, BitString signature)
{
// 1. If the public key is not at least eight bytes long, return INVALID.
if (publicKey.BitLength < 64)
{
return(new LmsVerificationResult("Validation failed. Public key wrong length."));
}
// 2. Parse pubtype, I, and T[1] from the public key as follows:
// a. pubtype = strTou32(first 4 bytes of public key)
var pubType = publicKey.MSBSubstring(0, 32);
// b. ots_typecode = strTou32(next 4 bytes of public key)
var ots_typecode = publicKey.MSBSubstring(32, 32);
// c. Set m according to pubtype, based on Table 2.
var m = LmsModeMapping.GetMFromCode(pubType);
// d. If the public key is not exactly 24 + m bytes long, return INVALID.
if (publicKey.BitLength != (24 + m) * 8)
{
return(new LmsVerificationResult("Validation failed. Public key wrong length."));
}
// e. I = next 16 bytes of the public key
var I = publicKey.MSBSubstring(64, 128);
// f. T[1] = next m bytes of the public key
var root = publicKey.MSBSubstring(192, m * 8);
// 3. Compute the LMS Public Key Candidate Tc from the signature, message, identifier,
// pubtype, and ots_typecode, using Algorithm 6a.
// Algorithm 6a:
// 1. If the signature is not at least eight bytes long, return INVALID.
if (signature.BitLength < 64)
{
return(new LmsVerificationResult("Validation failed. Signature wrong length."));
}
// 2. Parse sigtype, q, lmots_signature, and path from the signature as follows:
// a. q = strTou32(first 4 bytes of signature)
var q = signature.MSBSubstring(0, 32);
// b. otssigtype = strTou32(next 4 bytes of signature)
var otssigtype = signature.MSBSubstring(32, 32);
// c. If otssigtype is not the OTS typecode from the public key, return INVALID.
if (!otssigtype.Equals(ots_typecode))
{
return(new LmsVerificationResult("Validation failed. OTS Code incongruent."));
}
// d. Set n, p according to otssigtype and Table 1; if the signature is not
// at least 12 + n* (p + 1) bytes long, return INVALID.
var n = LmotsModeMapping.GetNFromCode(otssigtype);
var p = LmotsModeMapping.GetPFromCode(otssigtype);
if (signature.BitLength < (12 + n * (p - 1)) * 8)
{
return(new LmsVerificationResult("Validation failed. Signature wrong length."));
}
// e. lmots_signature = bytes 4 through 7 + n* (p + 1) of signature
var lmots_signature = signature.MSBSubstring(32, (4 + n * (p + 1)) * 8);
// f. sigtype = strTou32(bytes 8 + n* (p + 1)) through 11 + n* (p + 1) of signature)
var sigtype = signature.MSBSubstring((8 + n * (p + 1)) * 8, 32);
// g. If sigtype is not the LM typecode from the public key, return INVALID.
if (!sigtype.Equals(pubType))
{
return(new LmsVerificationResult("Verification failed. Type mismatch."));
}
// h. Set m, h according to sigtype and Table 2.
// m already set from above
var h = LmsModeMapping.GetHFromCode(sigtype);
// i. If q >= 2^h or the signature is not exactly 12 + n* (p + 1) + m* h bytes long, return INVALID.
if (q.ToPositiveBigInteger() >= (1 << h) || signature.BitLength != (12 + n * (p + 1) + m * h) * 8)
{
return(new LmsVerificationResult("Verification failed. Signature wrong length."));
}
// j. Set path as follows:
// path[0] = next m bytes of signature
// path[1] = next m bytes of signature
// ...
// path[h-1] = next m bytes of signature
var path = new BitString[h];
for (int i = 0; i < h; i++)
{
path[i] = signature.MSBSubstring(((12 + n * (p + 1)) * 8) + (i * m * 8), m * 8);
}
// 3. Kc = candidate public key computed by applying Algorithm 4b to the signature lmots_signature,
// the message, and the identifiers I, q
var Kc = _lmots.Algorithm4b(lmots_signature, msg, otssigtype, I, q);
if (Kc == null)
{
return(new LmsVerificationResult("Verification failed. Algorithm 4b failed."));
}
// 4. Compute the candidate LMS root value Tc as described in rfc 8554
var node_num = (1 << h) + q.ToPositiveBigInteger();
var tmp = _sha256.HashMessage(I
.ConcatenateBits(new BitString(node_num, 32))
.ConcatenateBits(D_LEAF)
.ConcatenateBits(Kc)).Digest;
for (int i = 0; node_num > 1; node_num /= 2)
{
if (node_num % 2 == 1)
{
tmp = _sha256.HashMessage(I
.ConcatenateBits(new BitString(node_num / 2, 32))
.ConcatenateBits(D_INTR)
.ConcatenateBits(path[i])
.ConcatenateBits(tmp)).Digest;
}
else
{
tmp = _sha256.HashMessage(I
.ConcatenateBits(new BitString(node_num / 2, 32))
.ConcatenateBits(D_INTR)
.ConcatenateBits(tmp)
.ConcatenateBits(path[i])).Digest;
}
i++;
}
// 5. Return Tc
var Tc = tmp;
// END Algorithm 6a
// 4. If Tc is equal to T[1], return VALID; otherwise, return INVALID.
if (Tc.Equals(root))
{
return(new LmsVerificationResult());
}
else
{
return(new LmsVerificationResult("Verification failed. Signature invalid."));
}
}