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[Private Key] Support more ciphers for OpenSSH private key decryption #1487

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Sep 10, 2024
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[Private Key] Support more ciphers for OpenSSH private key decryption #1487

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14 changes: 13 additions & 1 deletion README.md
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Expand Up @@ -101,14 +101,26 @@ The main types provided by this library are:
* ECDSA 256/384/521 in OpenSSL PEM format ("BEGIN EC PRIVATE KEY")
* ECDSA 256/384/521, ED25519 and RSA in OpenSSH key format ("BEGIN OPENSSH PRIVATE KEY")

Private keys can be encrypted using one of the following cipher methods:
Private keys in OpenSSL PEM and ssh.com format can be encrypted using one of the following cipher methods:
* DES-EDE3-CBC
* DES-EDE3-CFB
* DES-CBC
* AES-128-CBC
* AES-192-CBC
* AES-256-CBC

Private keys in OpenSSH key format can be encrypted using one of the following cipher methods:
* 3des-cbc
* aes128-cbc
* aes192-cbc
* aes256-cbc
* aes128-ctr
* aes192-ctr
* aes256-ctr
* aes128-gcm<span></span>@openssh.com
* aes256-gcm<span></span>@openssh.com
* chacha20-poly1305<span></span>@openssh.com

## Host Key Algorithms

**SSH.NET** supports the following host key algorithms:
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6 changes: 3 additions & 3 deletions src/Renci.SshNet/ConnectionInfo.cs
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Expand Up @@ -386,9 +386,9 @@ public ConnectionInfo(string host, int port, string username, ProxyTypes proxyTy
{ "aes128-ctr", new CipherInfo(128, (key, iv) => new AesCipher(key, iv, AesCipherMode.CTR, pkcs7Padding: false)) },
{ "aes192-ctr", new CipherInfo(192, (key, iv) => new AesCipher(key, iv, AesCipherMode.CTR, pkcs7Padding: false)) },
{ "aes256-ctr", new CipherInfo(256, (key, iv) => new AesCipher(key, iv, AesCipherMode.CTR, pkcs7Padding: false)) },
{ "aes128-gcm@openssh.com", new CipherInfo(128, (key, iv) => new AesGcmCipher(key, iv), isAead: true) },
{ "aes256-gcm@openssh.com", new CipherInfo(256, (key, iv) => new AesGcmCipher(key, iv), isAead: true) },
{ "chacha20-poly1305@openssh.com", new CipherInfo(512, (key, iv) => new ChaCha20Poly1305Cipher(key), isAead: true) },
{ "aes128-gcm@openssh.com", new CipherInfo(128, (key, iv) => new AesGcmCipher(key, iv, aadLength: 4), isAead: true) },
{ "aes256-gcm@openssh.com", new CipherInfo(256, (key, iv) => new AesGcmCipher(key, iv, aadLength: 4), isAead: true) },
{ "chacha20-poly1305@openssh.com", new CipherInfo(512, (key, iv) => new ChaCha20Poly1305Cipher(key, aadLength: 4), isAead: true) },
{ "aes128-cbc", new CipherInfo(128, (key, iv) => new AesCipher(key, iv, AesCipherMode.CBC, pkcs7Padding: false)) },
{ "aes192-cbc", new CipherInfo(192, (key, iv) => new AesCipher(key, iv, AesCipherMode.CBC, pkcs7Padding: false)) },
{ "aes256-cbc", new CipherInfo(256, (key, iv) => new AesCipher(key, iv, AesCipherMode.CBC, pkcs7Padding: false)) },
Expand Down
119 changes: 100 additions & 19 deletions src/Renci.SshNet/PrivateKeyFile.cs
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Expand Up @@ -39,7 +39,7 @@ namespace Renci.SshNet
/// </list>
/// </para>
/// <para>
/// The following encryption algorithms are supported:
/// The following encryption algorithms are supported for OpenSSL PEM and ssh.com format:
/// <list type="bullet">
/// <item>
/// <description>DES-EDE3-CBC</description>
Expand All @@ -60,6 +60,39 @@ namespace Renci.SshNet
/// <description>AES-256-CBC</description>
/// </item>
/// </list>
/// The following encryption algorithms are supported for OpenSSH format:
/// <list type="bullet">
/// <item>
/// <description>3des-cbc</description>
/// </item>
/// <item>
/// <description>aes128-cbc</description>
/// </item>
/// <item>
/// <description>aes192-cbc</description>
/// </item>
/// <item>
/// <description>aes256-cbc</description>
/// </item>
/// <item>
/// <description>aes128-ctr</description>
/// </item>
/// <item>
/// <description>aes192-ctr</description>
/// </item>
/// <item>
/// <description>aes256-ctr</description>
/// </item>
/// <item>
/// <description>aes128-gcm@openssh.com</description>
/// </item>
/// <item>
/// <description>aes256-gcm@openssh.com</description>
/// </item>
/// <item>
/// <description>chacha20-poly1305@openssh.com</description>
/// </item>
/// </list>
/// </para>
/// </remarks>
public partial class PrivateKeyFile : IPrivateKeySource, IDisposable
Expand Down Expand Up @@ -450,7 +483,17 @@ private static byte[] DecryptKey(CipherInfo cipherInfo, byte[] cipherData, strin

var cipher = cipherInfo.Cipher(cipherKey.ToArray(), binarySalt);

return cipher.Decrypt(cipherData);
try
{
return cipher.Decrypt(cipherData);
}
finally
{
if (cipher is IDisposable disposable)
{
disposable.Dispose();
}
}
}

/// <summary>
Expand All @@ -474,7 +517,7 @@ private static Key ParseOpenSshV1Key(byte[] keyFileData, string passPhrase)
throw new SshException("This openssh key does not contain the 'openssh-key-v1' format magic header");
}

// cipher will be "aes256-cbc" if using a passphrase, "none" otherwise
// cipher will be "aes256-cbc" or other cipher if using a passphrase, "none" otherwise
var cipherName = keyReader.ReadString(Encoding.UTF8);

// key derivation function (kdf): bcrypt or nothing
Expand Down Expand Up @@ -503,7 +546,7 @@ private static Key ParseOpenSshV1Key(byte[] keyFileData, string passPhrase)

// possibly encrypted private key
var privateKeyLength = (int)keyReader.ReadUInt32();
var privateKeyBytes = keyReader.ReadBytes(privateKeyLength);
byte[] privateKeyBytes;

// decrypt private key if necessary
if (cipherName != "none")
Expand All @@ -518,38 +561,76 @@ private static Key ParseOpenSshV1Key(byte[] keyFileData, string passPhrase)
throw new SshException("kdf " + kdfName + " is not supported for openssh key file");
}

// inspired by the SSHj library (https://github.com/hierynomus/sshj)
// apply the kdf to derive a key and iv from the passphrase
var passPhraseBytes = Encoding.UTF8.GetBytes(passPhrase);
var keyiv = new byte[48];
new BCrypt().Pbkdf(passPhraseBytes, salt, rounds, keyiv);
var key = new byte[32];
Array.Copy(keyiv, 0, key, 0, 32);
var iv = new byte[16];
Array.Copy(keyiv, 32, iv, 0, 16);

AesCipher cipher;
var ivLength = 16;
CipherInfo cipherInfo;
switch (cipherName)
{
case "3des-cbc":
ivLength = 8;
cipherInfo = new CipherInfo(192, (key, iv) => new TripleDesCipher(key, new CbcCipherMode(iv), padding: null));
break;
case "aes128-cbc":
cipherInfo = new CipherInfo(128, (key, iv) => new AesCipher(key, iv, AesCipherMode.CBC, pkcs7Padding: false));
break;
case "aes192-cbc":
cipherInfo = new CipherInfo(192, (key, iv) => new AesCipher(key, iv, AesCipherMode.CBC, pkcs7Padding: false));
break;
case "aes256-cbc":
cipher = new AesCipher(key, iv, AesCipherMode.CBC, pkcs7Padding: false);
cipherInfo = new CipherInfo(256, (key, iv) => new AesCipher(key, iv, AesCipherMode.CBC, pkcs7Padding: false));
break;
case "aes128-ctr":
cipherInfo = new CipherInfo(128, (key, iv) => new AesCipher(key, iv, AesCipherMode.CTR, pkcs7Padding: false));
break;
case "aes192-ctr":
cipherInfo = new CipherInfo(192, (key, iv) => new AesCipher(key, iv, AesCipherMode.CTR, pkcs7Padding: false));
break;
case "aes256-ctr":
cipher = new AesCipher(key, iv, AesCipherMode.CTR, pkcs7Padding: false);
cipherInfo = new CipherInfo(256, (key, iv) => new AesCipher(key, iv, AesCipherMode.CTR, pkcs7Padding: false));
break;
case "aes128-gcm@openssh.com":
cipherInfo = new CipherInfo(128, (key, iv) => new AesGcmCipher(key, iv, aadLength: 0), isAead: true);
break;
case "aes256-gcm@openssh.com":
cipherInfo = new CipherInfo(256, (key, iv) => new AesGcmCipher(key, iv, aadLength: 0), isAead: true);
break;
case "chacha20-poly1305@openssh.com":
ivLength = 12;
cipherInfo = new CipherInfo(256, (key, iv) => new ChaCha20Poly1305Cipher(key, aadLength: 0), isAead: true);
break;
default:
throw new SshException("Cipher '" + cipherName + "' is not supported for an OpenSSH key.");
}

var keyLength = cipherInfo.KeySize / 8;

// inspired by the SSHj library (https://github.com/hierynomus/sshj)
// apply the kdf to derive a key and iv from the passphrase
var passPhraseBytes = Encoding.UTF8.GetBytes(passPhrase);
var keyiv = new byte[keyLength + ivLength];
new BCrypt().Pbkdf(passPhraseBytes, salt, rounds, keyiv);

var key = keyiv.Take(keyLength);
var iv = keyiv.Take(keyLength, ivLength);

var cipher = cipherInfo.Cipher(key, iv);
var cipherData = keyReader.ReadBytes(privateKeyLength + cipher.TagSize);
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try
{
privateKeyBytes = cipher.Decrypt(privateKeyBytes);
privateKeyBytes = cipher.Decrypt(cipherData, 0, privateKeyLength);
}
finally
{
cipher.Dispose();
if (cipher is IDisposable disposable)
{
disposable.Dispose();
}
}
}
else
{
privateKeyBytes = keyReader.ReadBytes(privateKeyLength);
}

// validate private key length
privateKeyLength = privateKeyBytes.Length;
Expand Down
34 changes: 16 additions & 18 deletions src/Renci.SshNet/Security/Cryptography/Ciphers/AesGcmCipher.cs
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Expand Up @@ -12,9 +12,9 @@ namespace Renci.SshNet.Security.Cryptography.Ciphers
/// </summary>
internal sealed partial class AesGcmCipher : SymmetricCipher, IDisposable
{
private const int PacketLengthFieldLength = 4;
private const int TagSizeInBytes = 16;
private readonly byte[] _iv;
private readonly int _aadLength;
#if NET6_0_OR_GREATER
private readonly Impl _impl;
#else
Expand Down Expand Up @@ -55,11 +55,13 @@ public override int TagSize
/// </summary>
/// <param name="key">The key.</param>
/// <param name="iv">The IV.</param>
public AesGcmCipher(byte[] key, byte[] iv)
/// <param name="aadLength">The length of additional associated data.</param>
public AesGcmCipher(byte[] key, byte[] iv, int aadLength)
: base(key)
{
// SSH AES-GCM requires a 12-octet Initial IV
_iv = iv.Take(12);
_aadLength = aadLength;
#if NET6_0_OR_GREATER
if (System.Security.Cryptography.AesGcm.IsSupported)
{
Expand All @@ -78,32 +80,30 @@ public AesGcmCipher(byte[] key, byte[] iv)
/// <param name="input">
/// The input data with below format:
/// <code>
/// [outbound sequence field][packet length field][padding length field sz][payload][random paddings]
/// [----4 bytes----(offset)][------4 bytes------][----------------Plain Text---------------(length)]
/// [----(offset)][----AAD----][----Plain Text----(length)]
/// </code>
/// </param>
/// <param name="offset">The zero-based offset in <paramref name="input"/> at which to begin encrypting.</param>
/// <param name="length">The number of bytes to encrypt from <paramref name="input"/>.</param>
/// <returns>
/// The encrypted data with below format:
/// <code>
/// [packet length field][padding length field sz][payload][random paddings][Authenticated TAG]
/// [------4 bytes------][------------------Cipher Text--------------------][-------TAG-------]
/// [----AAD----][----Cipher Text----][----TAG----]
/// </code>
/// </returns>
public override byte[] Encrypt(byte[] input, int offset, int length)
{
var output = new byte[length + TagSize];
Buffer.BlockCopy(input, offset, output, 0, PacketLengthFieldLength);
Buffer.BlockCopy(input, offset, output, 0, _aadLength);

_impl.Encrypt(
input,
plainTextOffset: offset + PacketLengthFieldLength,
plainTextLength: length - PacketLengthFieldLength,
plainTextOffset: offset + _aadLength,
plainTextLength: length - _aadLength,
associatedDataOffset: offset,
associatedDataLength: PacketLengthFieldLength,
associatedDataLength: _aadLength,
output,
cipherTextOffset: PacketLengthFieldLength);
cipherTextOffset: _aadLength);

IncrementCounter();

Expand All @@ -116,31 +116,29 @@ public override byte[] Encrypt(byte[] input, int offset, int length)
/// <param name="input">
/// The input data with below format:
/// <code>
/// [inbound sequence field][packet length field][padding length field sz][payload][random paddings][Authenticated TAG]
/// [--------4 bytes-------][--4 bytes--(offset)][--------------Cipher Text----------------(length)][-------TAG-------]
/// [----][----AAD----(offset)][----Cipher Text----(length)][----TAG----]
/// </code>
/// </param>
/// <param name="offset">The zero-based offset in <paramref name="input"/> at which to begin decrypting and authenticating.</param>
/// <param name="length">The number of bytes to decrypt and authenticate from <paramref name="input"/>.</param>
/// <returns>
/// The decrypted data with below format:
/// <code>
/// [padding length field sz][payload][random paddings]
/// [--------------------Plain Text-------------------]
/// [----Plain Text----]
/// </code>
/// </returns>
public override byte[] Decrypt(byte[] input, int offset, int length)
{
Debug.Assert(offset == 8, "The offset must be 8");
Debug.Assert(offset >= _aadLength, "The offset must be greater than or equals to aad length");

var output = new byte[length];

_impl.Decrypt(
input,
cipherTextOffset: offset,
cipherTextLength: length,
associatedDataOffset: offset - PacketLengthFieldLength,
associatedDataLength: PacketLengthFieldLength,
associatedDataOffset: offset - _aadLength,
associatedDataLength: _aadLength,
output,
plainTextOffset: 0);

Expand Down
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