# < Summary

Information

Class: | Renci.SshNet.Security.Cryptography.DsaDigitalSignature
Assembly: | Renci.SshNet
File(s): | \home\appveyor\projects\ssh-net\src\Renci.SshNet\Security\Cryptography\DsaDigitalSignature.cs

Line coverage
71%

Covered lines: | 62
Uncovered lines: | 25
Coverable lines: | 87
Total lines: | 205
Line coverage: | 71.2%

Branch coverage
63%

Covered branches: | 19
Total branches: | 30
Branch coverage: | 63.3%

Method coverage

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# Metrics

Method | Branch coverage | Cyclomatic complexity | Line coverage
--- | --- | --- | ---
.ctor(...) | 50% | 2 | 75%
Verify(...) | 58.33% | 12 | 79.31%
Sign(...) | 90% | 10 | 92.85%
Dispose() | 100% | 1 | 0%
Dispose(...) | 33.33% | 6 | 26.66%
Finalize() | 100% | 1 | 100%

# File(s)

## \home\appveyor\projects\ssh-net\src\Renci.SshNet\Security\Cryptography\DsaDigitalSignature.cs

| # | Line |  | Line coverage
--- | --- | --- | --- | ---
|  | `1` |  | `using System;`
|  | `2` |  | `using System.Security.Cryptography;`
|  | `3` |  | ``
|  | `4` |  | `using Renci.SshNet.Abstractions;`
|  | `5` |  | `using Renci.SshNet.Common;`
|  | `6` |  | ``
|  | `7` |  | `namespace Renci.SshNet.Security.Cryptography`
|  | `8` |  | `{`
|  | `9` |  | `/// <summary>`
|  | `10` |  | `/// Implements DSA digital signature algorithm.`
|  | `11` |  | `/// </summary>`
|  | `12` |  | `public class DsaDigitalSignature : DigitalSignature, IDisposable`
|  | `13` |  | `{`
|  | `14` |  | `private readonly DsaKey _key;`
|  | `15` |  | `private HashAlgorithm _hash;`
|  | `16` |  | `private bool _isDisposed;`
|  | `17` |  | ``
|  | `18` |  | `/// <summary>`
|  | `19` |  | `/// Initializes a new instance of the <see cref="DsaDigitalSignature" /> class.`
|  | `20` |  | `/// </summary>`
|  | `21` |  | `/// <param name="key">The DSA key.</param>`
|  | `22` |  | `/// <exception cref="ArgumentNullException"><paramref name="key"/> is <see langword="null"/>.</exception>`
| 16 | `23` |  | `public DsaDigitalSignature(DsaKey key)`
| 16 | `24` |  | `{`
| 16 | `25` |  | `if (key is null)`
| 0 | `26` |  | `{`
| 0 | `27` |  | `throw new ArgumentNullException(nameof(key));`
|  | `28` |  | `}`
|  | `29` |  | ``
| 16 | `30` |  | `_key = key;`
|  | `31` |  | ``
| 16 | `32` |  | `_hash = CryptoAbstraction.CreateSHA1();`
| 16 | `33` |  | `}`
|  | `34` |  | ``
|  | `35` |  | `/// <summary>`
|  | `36` |  | `/// Verifies the signature.`
|  | `37` |  | `/// </summary>`
|  | `38` |  | `/// <param name="input">The input.</param>`
|  | `39` |  | `/// <param name="signature">The signature.</param>`
|  | `40` |  | `/// <returns>`
|  | `41` |  | `/// <see langword="true"/> if signature was successfully verified; otherwise <see langword="false"/>.`
|  | `42` |  | `/// </returns>`
|  | `43` |  | `/// <exception cref="InvalidOperationException">Invalid signature.</exception>`
|  | `44` |  | `public override bool Verify(byte[] input, byte[] signature)`
| 3 | `45` |  | `{`
| 3 | `46` |  | `var hashInput = _hash.ComputeHash(input);`
|  | `47` |  | ``
| 3 | `48` |  | `var hm = new BigInteger(hashInput.Reverse().Concat(new byte[] { 0 }));`
|  | `49` |  | ``
| 3 | `50` |  | `if (signature.Length != 40)`
| 0 | `51` |  | `{`
| 0 | `52` |  | `throw new InvalidOperationException("Invalid signature.");`
|  | `53` |  | `}`
|  | `54` |  | ``
|  | `55` |  | `// Extract r and s numbers from the signature`
| 3 | `56` |  | `var rBytes = new byte[21];`
| 3 | `57` |  | `var sBytes = new byte[21];`
|  | `58` |  | ``
| 189 | `59` |  | `for (int i = 0, j = 20; i < 20; i++, j--)`
| 60 | `60` |  | `{`
| 60 | `61` |  | `rBytes[i] = signature[j - 1];`
| 60 | `62` |  | `sBytes[i] = signature[j + 20 - 1];`
| 60 | `63` |  | `}`
|  | `64` |  | ``
| 3 | `65` |  | `var r = new BigInteger(rBytes);`
| 3 | `66` |  | `var s = new BigInteger(sBytes);`
|  | `67` |  | ``
|  | `68` |  | `// Reject the signature if 0 < r < q or 0 < s < q is not satisfied.`
| 3 | `69` |  | `if (r <= 0 || r >= _key.Q)`
| 0 | `70` |  | `{`
| 0 | `71` |  | `return false;`
|  | `72` |  | `}`
|  | `73` |  | ``
| 3 | `74` |  | `if (s <= 0 || s >= _key.Q)`
| 0 | `75` |  | `{`
| 0 | `76` |  | `return false;`
|  | `77` |  | `}`
|  | `78` |  | ``
|  | `79` |  | `// Calculate w = s−1 mod q`
| 3 | `80` |  | `var w = BigInteger.ModInverse(s, _key.Q);`
|  | `81` |  | ``
|  | `82` |  | `// Calculate u1 = H(m)·w mod q`
| 3 | `83` |  | `var u1 = (hm * w) % _key.Q;`
|  | `84` |  | ``
|  | `85` |  | `// Calculate u2 = r * w mod q`
| 3 | `86` |  | `var u2 = (r * w) % _key.Q;`
|  | `87` |  | ``
| 3 | `88` |  | `u1 = BigInteger.ModPow(_key.G, u1, _key.P);`
| 3 | `89` |  | `u2 = BigInteger.ModPow(_key.Y, u2, _key.P);`
|  | `90` |  | ``
|  | `91` |  | `// Calculate v = ((g pow u1 * y pow u2) mod p) mod q`
| 3 | `92` |  | `var v = ((u1 * u2) % _key.P) % _key.Q;`
|  | `93` |  | ``
|  | `94` |  | `// The signature is valid if v = r`
| 3 | `95` |  | `return v == r;`
| 3 | `96` |  | `}`
|  | `97` |  | ``
|  | `98` |  | `/// <summary>`
|  | `99` |  | `/// Creates the signature.`
|  | `100` |  | `/// </summary>`
|  | `101` |  | `/// <param name="input">The input.</param>`
|  | `102` |  | `/// <returns>`
|  | `103` |  | `/// Signed input data.`
|  | `104` |  | `/// </returns>`
|  | `105` |  | `/// <exception cref="SshException">Invalid DSA key.</exception>`
|  | `106` |  | `public override byte[] Sign(byte[] input)`
| 1 | `107` |  | `{`
| 1 | `108` |  | `var hashInput = _hash.ComputeHash(input);`
|  | `109` |  | ``
| 1 | `110` |  | `var m = new BigInteger(hashInput.Reverse().Concat(new byte[] { 0 }));`
|  | `111` |  | ``
|  | `112` |  | `BigInteger s;`
|  | `113` |  | `BigInteger r;`
|  | `114` |  | ``
|  | `115` |  | `do`
| 1 | `116` |  | `{`
| 1 | `117` |  | `var k = BigInteger.Zero;`
|  | `118` |  | ``
|  | `119` |  | `do`
| 1 | `120` |  | `{`
|  | `121` |  | `// Generate a random per-message value k where 0 < k < q`
| 1 | `122` |  | `var bitLength = _key.Q.BitLength;`
|  | `123` |  | ``
| 1 | `124` |  | `if (_key.Q < BigInteger.Zero)`
| 0 | `125` |  | `{`
| 0 | `126` |  | `throw new SshException("Invalid DSA key.");`
|  | `127` |  | `}`
|  | `128` |  | ``
| 2 | `129` |  | `while (k <= 0 || k >= _key.Q)`
| 1 | `130` |  | `{`
| 1 | `131` |  | `k = BigInteger.Random(bitLength);`
| 1 | `132` |  | `}`
|  | `133` |  | ``
|  | `134` |  | `// Calculate r = ((g pow k) mod p) mod q`
| 1 | `135` |  | `r = BigInteger.ModPow(_key.G, k, _key.P) % _key.Q;`
|  | `136` |  | ``
|  | `137` |  | `// In the unlikely case that r = 0, start again with a different random k`
| 1 | `138` |  | `}`
| 1 | `139` |  | `while (r.IsZero);`
|  | `140` |  | ``
|  | `141` |  | `// Calculate s = ((k pow −1)(H(m) + x*r)) mod q`
| 1 | `142` |  | `k = BigInteger.ModInverse(k, _key.Q) * (m + (_key.X * r));`
|  | `143` |  | ``
| 1 | `144` |  | `s = k % _key.Q;`
|  | `145` |  | ``
|  | `146` |  | `// In the unlikely case that s = 0, start again with a different random k`
| 1 | `147` |  | `}`
| 1 | `148` |  | `while (s.IsZero);`
|  | `149` |  | ``
|  | `150` |  | `// The signature is (r, s)`
| 1 | `151` |  | `var signature = new byte[40];`
|  | `152` |  | ``
|  | `153` |  | `// issue #1918: pad part with zero's on the left if length is less than 20`
| 1 | `154` |  | `var rBytes = r.ToByteArray().Reverse().TrimLeadingZeros();`
| 1 | `155` |  | `Array.Copy(rBytes, 0, signature, 20 - rBytes.Length, rBytes.Length);`
|  | `156` |  | ``
|  | `157` |  | `// issue #1918: pad part with zero's on the left if length is less than 20`
| 1 | `158` |  | `var sBytes = s.ToByteArray().Reverse().TrimLeadingZeros();`
| 1 | `159` |  | `Array.Copy(sBytes, 0, signature, 40 - sBytes.Length, sBytes.Length);`
|  | `160` |  | ``
| 1 | `161` |  | `return signature;`
| 1 | `162` |  | `}`
|  | `163` |  | ``
|  | `164` |  | `/// <summary>`
|  | `165` |  | `/// Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.`
|  | `166` |  | `/// </summary>`
|  | `167` |  | `public void Dispose()`
| 0 | `168` |  | `{`
| 0 | `169` |  | `Dispose(disposing: true);`
| 0 | `170` |  | `GC.SuppressFinalize(this);`
| 0 | `171` |  | `}`
|  | `172` |  | ``
|  | `173` |  | `/// <summary>`
|  | `174` |  | `/// Releases unmanaged and - optionally - managed resources.`
|  | `175` |  | `/// </summary>`
|  | `176` |  | `/// <param name="disposing"><see langword="true"/> to release both managed and unmanaged resources; <see langwor`
|  | `177` |  | `protected virtual void Dispose(bool disposing)`
| 16 | `178` |  | `{`
| 16 | `179` |  | `if (_isDisposed)`
| 0 | `180` |  | `{`
| 0 | `181` |  | `return;`
|  | `182` |  | `}`
|  | `183` |  | ``
| 16 | `184` |  | `if (disposing)`
| 0 | `185` |  | `{`
| 0 | `186` |  | `var hash = _hash;`
| 0 | `187` |  | `if (hash != null)`
| 0 | `188` |  | `{`
| 0 | `189` |  | `hash.Dispose();`
| 0 | `190` |  | `_hash = null;`
| 0 | `191` |  | `}`
|  | `192` |  | ``
| 0 | `193` |  | `_isDisposed = true;`
| 0 | `194` |  | `}`
| 16 | `195` |  | `}`
|  | `196` |  | ``
|  | `197` |  | `/// <summary>`
|  | `198` |  | `/// Finalizes an instance of the <see cref="DsaDigitalSignature"/> class.`
|  | `199` |  | `/// </summary>`
|  | `200` |  | `~DsaDigitalSignature()`
| 32 | `201` |  | `{`
| 16 | `202` |  | `Dispose(disposing: false);`
| 32 | `203` |  | `}`
|  | `204` |  | `}`
|  | `205` |  | `}`

# Methods/Properties

.ctor(Renci.SshNet.Security.DsaKey)
Verify(System.Byte[],System.Byte[])
Sign(System.Byte[])
Dispose()
Dispose(System.Boolean)
Finalize()