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Pad RSA signatures which have leading zeroes removed #1855

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4 changes: 3 additions & 1 deletion src/Renci.SshNet/Security/Cryptography/RsaDigitalSignature.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,8 @@
using System;
using System.Security.Cryptography;

using Renci.SshNet.Common;

namespace Renci.SshNet.Security.Cryptography
{
/// <summary>
Expand Down Expand Up @@ -35,7 +37,7 @@ public RsaDigitalSignature(RsaKey rsaKey, HashAlgorithmName hashAlgorithmName)
/// <inheritdoc/>
public override bool Verify(byte[] input, byte[] signature)
{
return _key.RSA.VerifyData(input, signature, _hashAlgorithmName, RSASignaturePadding.Pkcs1);
return _key.RSA.VerifyData(input, signature.Pad((_key.RSA.KeySize + 7) / 8), _hashAlgorithmName, RSASignaturePadding.Pkcs1);
}

/// <inheritdoc/>
Expand Down
48 changes: 30 additions & 18 deletions test/Renci.SshNet.Tests/Classes/Security/Cryptography/RsaDigitalSignatureTest.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,8 @@

using Microsoft.VisualStudio.TestTools.UnitTesting;


using Renci.SshNet.Common;
using Renci.SshNet.Security;
using Renci.SshNet.Security.Cryptography;
using Renci.SshNet.Tests.Common;
Expand Down Expand Up @@ -126,11 +128,13 @@ public void Sha512_SignAndVerify()
}

[TestMethod]
public void SignatureDoesNotTruncateLeadingZeroes()
public void SignatureLeadingZeroes()
{
// When signing, do not shorten signatures by truncating leading zeroes.
// Shortened/unpadded signatures are accepted by some servers but not all.
// A regression test for https://github.com/sshnet/SSH.NET/issues/1388

byte[] data = { 0x41, 0xdb, 0xf3, 0x09, 0x56 };
byte[] data = { 0xe3, 0x1a, 0xb1, 0x33, 0x30 };

RsaKey rsaKey = GetRsaKey();

Expand All @@ -140,25 +144,33 @@ public void SignatureDoesNotTruncateLeadingZeroes()

CollectionAssert.AreEqual(new byte[]
{
0x00, 0xa8, 0x35, 0x24, 0xc8, 0xc1, 0x94, 0x97, 0xc3, 0xdf, 0x94, 0x32, 0x62, 0xf2, 0x12, 0x57,
0x49, 0x22, 0x7e, 0x52, 0xfe, 0x6e, 0x23, 0x1f, 0x28, 0x84, 0xf9, 0x3e, 0x16, 0xda, 0xc3, 0x6f,
0xa0, 0xa4, 0x00, 0x9a, 0x9b, 0xf2, 0x3e, 0xf5, 0x47, 0x3a, 0x7a, 0x8a, 0xd1, 0x1e, 0xf1, 0xd0,
0x0b, 0x4d, 0x04, 0x16, 0x6f, 0x29, 0xf1, 0xe7, 0x26, 0xfd, 0x5a, 0x6e, 0x9a, 0xc4, 0x53, 0x7f,
0xbe, 0xa3, 0x3b, 0xa0, 0x95, 0x02, 0xe2, 0xcd, 0xd9, 0xa1, 0x4d, 0xae, 0x63, 0x4f, 0x95, 0x5e,
0x4f, 0xd6, 0x34, 0x3a, 0x05, 0x93, 0xcb, 0xb4, 0x18, 0xd2, 0xd0, 0xd6, 0x5f, 0x8c, 0xe3, 0x77,
0xca, 0x7f, 0x88, 0xfb, 0x72, 0x00, 0x00, 0x74, 0x31, 0xb7, 0xc5, 0xe8, 0xe2, 0x92, 0xf9, 0xab,
0x63, 0x8f, 0x87, 0x07, 0xc5, 0x90, 0xf2, 0xdd, 0x6d, 0xc6, 0x38, 0xee, 0x19, 0x65, 0x05, 0xa8,
0xda, 0xfc, 0x32, 0xe9, 0xbf, 0x2a, 0x0d, 0x6b, 0x2b, 0xac, 0x92, 0x48, 0xda, 0x3b, 0x8f, 0x4f,
0x68, 0x58, 0xa6, 0xa0, 0xcb, 0xdc, 0x44, 0xe3, 0x12, 0x12, 0xb3, 0x0a, 0xf2, 0x4c, 0xa6, 0x17,
0xab, 0xdb, 0x5b, 0x79, 0x63, 0x83, 0x8b, 0x10, 0x1c, 0x13, 0xc7, 0xf1, 0x15, 0x88, 0xc6, 0x92,
0xcd, 0x6f, 0x81, 0xde, 0x02, 0x1d, 0x35, 0x91, 0xf4, 0x0c, 0x66, 0xe6, 0x7c, 0x3f, 0x02, 0x98,
0xa7, 0x79, 0x6c, 0x90, 0x67, 0x14, 0x80, 0x18, 0xeb, 0xe7, 0x52, 0x44, 0x6b, 0x1b, 0x24, 0xac,
0x71, 0xaa, 0xde, 0xeb, 0xf7, 0x3c, 0xfc, 0xc0, 0x46, 0x23, 0x40, 0x2f, 0xb0, 0xf2, 0x0b, 0x2e,
0xfd, 0xd6, 0xd5, 0x2b, 0x3f, 0x00, 0xd8, 0xfe, 0x30, 0xa6, 0x67, 0xbc, 0x3d, 0xad, 0xb2, 0xf4,
0xf3, 0x98, 0xb5, 0x0a, 0x91, 0xf3, 0x9d, 0xfb, 0xe8, 0xeb, 0xe0, 0x35, 0x5b, 0x11, 0xcf, 0xdb,
0x00, 0x00, 0xc4, 0xa1, 0xa4, 0x63, 0xbd, 0x7c, 0xe7, 0x6e, 0xda, 0xb1, 0xee, 0x37, 0x61, 0x12,
0x86, 0xa4, 0x4a, 0xed, 0x28, 0x42, 0x84, 0xc3, 0xc9, 0x73, 0xff, 0x99, 0x56, 0x40, 0xee, 0x8f,
0x32, 0x4b, 0x3b, 0x6f, 0x2d, 0xeb, 0xcc, 0x6a, 0x2d, 0x54, 0x65, 0x97, 0x6f, 0xf0, 0xbc, 0x29,
0xb9, 0xdc, 0x46, 0xea, 0x0a, 0xf8, 0xce, 0xae, 0xd2, 0x52, 0x47, 0xc0, 0x63, 0xdb, 0xb5, 0x6d,
0xcd, 0xd8, 0xa3, 0xcb, 0x24, 0x11, 0xdd, 0x72, 0xdd, 0x1a, 0x63, 0x8a, 0xfb, 0xe3, 0xb5, 0x37,
0x7f, 0x6a, 0x5d, 0xbc, 0x0d, 0x93, 0x8c, 0x82, 0xcc, 0xf5, 0x88, 0xe1, 0x0d, 0xde, 0xe8, 0x68,
0x3b, 0x5c, 0x79, 0xd3, 0xd6, 0x34, 0x46, 0x2a, 0x14, 0x18, 0x14, 0xb6, 0x08, 0x8e, 0x1e, 0xf9,
0x58, 0xfc, 0x11, 0xd2, 0x88, 0xdc, 0x6c, 0x9c, 0x90, 0xa0, 0xaf, 0x11, 0x98, 0x47, 0x3e, 0x56,
0x6a, 0x10, 0x5d, 0x15, 0x08, 0x7e, 0xba, 0x82, 0x29, 0x3c, 0x44, 0xb9, 0x33, 0xe4, 0x51, 0x8a,
0xaa, 0x5a, 0x45, 0xb1, 0xbd, 0x4f, 0xce, 0x98, 0x3b, 0x79, 0x9c, 0x33, 0xb5, 0x2c, 0xa0, 0xa1,
0x15, 0x0b, 0x15, 0x47, 0xb6, 0x31, 0x94, 0xb0, 0xdb, 0xdb, 0x53, 0x22, 0x1f, 0xe6, 0x96, 0x88,
0x41, 0xbc, 0x6f, 0x02, 0x1b, 0xa2, 0x7e, 0xc7, 0x66, 0x06, 0x4b, 0x14, 0xc5, 0xd7, 0x90, 0x68,
0x87, 0x9e, 0xbe, 0x69, 0xaa, 0xd9, 0x5a, 0xda, 0x34, 0x11, 0x82, 0x24, 0x8c, 0x36, 0x3f, 0x44,
0x43, 0x19, 0x74, 0xe7, 0x17, 0xaf, 0x35, 0xca, 0x9c, 0xdd, 0x4c, 0xd2, 0x1a, 0xdf, 0x02, 0x26,
0xe7, 0x42, 0xbb, 0x3c, 0x21, 0xf4, 0xb2, 0xf8, 0x50, 0x7d, 0x98, 0x9c, 0x5d, 0xfa, 0x1e, 0x01,
0x2a, 0xb3, 0x6a, 0x11, 0xf8, 0x3d, 0x0b, 0xf1, 0xd0, 0x75, 0x46, 0xd3, 0x21, 0xa9, 0x10, 0xb7,
}, signedBytes);

Assert.IsTrue(digitalSignature.Verify(data, signedBytes));

// We are lenient in the opposite direction, allowing unpadded signatures.
Assert.IsTrue(digitalSignature.Verify(data, signedBytes.TrimLeadingZeros()));

signedBytes[2] = 0x00;

Assert.IsFalse(digitalSignature.Verify(data, signedBytes));
Assert.IsFalse(digitalSignature.Verify(data, signedBytes.TrimLeadingZeros()));
}

private static RsaKey GetRsaKey()
Expand Down