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Use DSASignatureFormat in Secp256r1SignatureGenerator #67

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Use DSASignatureFormat in Secp256r1SignatureGenerator #67

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98 changes: 10 additions & 88 deletions src/net-questdb-client/Secp256r1SignatureGenerator.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -22,95 +22,17 @@ public class Secp256r1SignatureGenerator
/// <returns></returns>
public byte[] GenerateSignature(byte[] privateKey, byte[] buffer, int bufferLen)
{
using var ecdsa = ECDsa.Create(ECCurve.NamedCurves.nistP256);

var ecParameters = new ECParameters
using var ecdsa = ECDsa.Create(new ECParameters
{
Curve = ECCurve.NamedCurves.nistP256,
D = privateKey,
};

ecdsa.ImportParameters(ecParameters);

var ieeeSignature = ecdsa.SignData(buffer, 0, bufferLen, HashAlgorithmName.SHA256);

// Convert to DER format for Java compatibility
return ConvertIeeeP1363ToDer(ieeeSignature);
}

private byte[] ConvertIeeeP1363ToDer(byte[] ieeeSignature)
{
var halfLength = ieeeSignature.Length / 2;

// Calculate sizes without allocating intermediate arrays
var rStart = GetLeadingZeroCountConstantTime(ieeeSignature, 0, halfLength);
var sStart = GetLeadingZeroCountConstantTime(ieeeSignature, halfLength, halfLength);

var rLength = halfLength - rStart;
var sLength = halfLength - sStart;

// Check if we need padding for negative values
var rNeedsPadding = rLength > 0 && (ieeeSignature[rStart] & 0x80) != 0;
var sNeedsPadding = sLength > 0 && (ieeeSignature[halfLength + sStart] & 0x80) != 0;

var rEncodedLength = rLength + (rNeedsPadding ? 1 : 0);
var sEncodedLength = sLength + (sNeedsPadding ? 1 : 0);

// Calculate total DER size
var rDerSize = 2 + rEncodedLength; // tag + length + value
var sDerSize = 2 + sEncodedLength; // tag + length + value
var totalContentSize = rDerSize + sDerSize;
var totalSize = 2 + totalContentSize; // sequence tag + length + content

// Single allocation for the final result
var result = new byte[totalSize];
var pos = 0;

// Write SEQUENCE header
result[pos++] = 0x30; // SEQUENCE tag
result[pos++] = (byte)totalContentSize;

// Write r INTEGER
result[pos++] = 0x02; // INTEGER tag
result[pos++] = (byte)rEncodedLength;

if (rNeedsPadding)
{
result[pos++] = 0x00;
}

// Copy r value directly
Array.Copy(ieeeSignature, rStart, result, pos, rLength);
pos += rLength;

// Write s INTEGER
result[pos++] = 0x02; // INTEGER tag
result[pos++] = (byte)sEncodedLength;

if (sNeedsPadding)
{
result[pos++] = 0x00;
}

// Copy s value directly
Array.Copy(ieeeSignature, halfLength + sStart, result, pos, sLength);

return result;
}

// Constant-time leading zero count to prevent timing attacks
private static int GetLeadingZeroCountConstantTime(byte[] array, int offset, int length)
{
var count = 0;
var end = offset + length - 1;

for (var i = offset; i < end; i++)
{
var isZero = array[i] == 0 ? 1 : 0;
var shouldCount = count == i - offset ? 1 : 0;
count += isZero & shouldCount;
}

return count;
D = privateKey,
});

return ecdsa.SignData(
buffer,
0,
bufferLen,
HashAlgorithmName.SHA256,
DSASignatureFormat.Rfc3279DerSequence);
}
}