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Support for encrypt-then-mac

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This commit is contained in:
Kyle Spearrin 2016-12-10 22:05:52 -05:00
parent 9879f7fa0a
commit 7bc38a35e8
2 changed files with 66 additions and 8 deletions
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29
src/App/Models/CipherString.cs
View File

@ -18,7 +18,7 @@ namespace Bit.App.Models
EncryptedString = encryptedString;
}
public CipherString(string initializationVector, string cipherText)
public CipherString(string initializationVector, string cipherText, string mac = null)
{
if(string.IsNullOrWhiteSpace(initializationVector))
{
@ -31,13 +31,32 @@ namespace Bit.App.Models
}
EncryptedString = string.Format("{0}|{1}", initializationVector, cipherText);
if(!string.IsNullOrWhiteSpace(mac))
{
EncryptedString = string.Format("{0}|{1}", EncryptedString, mac);
}
}
public string EncryptedString { get; private set; }
public string InitializationVector { get { return EncryptedString?.Split('|')[0]; } }
public string CipherText { get { return EncryptedString?.Split('|')[1]; } }
public byte[] InitializationVectorBytes { get { return Convert.FromBase64String(InitializationVector); } }
public byte[] CipherTextBytes { get { return Convert.FromBase64String(CipherText); } }
public string InitializationVector => EncryptedString?.Split('|')[0] ?? null;
public string CipherText => EncryptedString?.Split('|')[1] ?? null;
public string Mac
{
get
{
var pieces = EncryptedString?.Split('|') ?? new string[0];
if(pieces.Length > 2)
{
return pieces[2];
}
return null;
}
}
public byte[] InitializationVectorBytes => Convert.FromBase64String(InitializationVector);
public byte[] CipherTextBytes => Convert.FromBase64String(CipherText);
public byte[] MacBytes => Mac == null ? null : Convert.FromBase64String(Mac);
public string Decrypt()
{

45
src/App/Services/CryptoService.cs
View File

@ -106,6 +106,9 @@ namespace Bit.App.Services
}
}
public byte[] EncKey => Key?.Take(16).ToArray();
public byte[] MacKey => Key?.Skip(16).Take(16).ToArray();
public CipherString Encrypt(string plaintextValue)
{
if(Key == null)
@ -121,10 +124,14 @@ namespace Bit.App.Services
var plaintextBytes = Encoding.UTF8.GetBytes(plaintextValue);
var provider = WinRTCrypto.SymmetricKeyAlgorithmProvider.OpenAlgorithm(SymmetricAlgorithm.AesCbcPkcs7);
var cryptoKey = provider.CreateSymmetricKey(Key);
// TODO: Turn on whenever ready to support encrypt-then-mac
var cryptoKey = provider.CreateSymmetricKey(false ? EncKey : Key);
var iv = WinRTCrypto.CryptographicBuffer.GenerateRandom(provider.BlockLength);
var encryptedBytes = WinRTCrypto.CryptographicEngine.Encrypt(cryptoKey, plaintextBytes, iv);
return new CipherString(Convert.ToBase64String(iv), Convert.ToBase64String(encryptedBytes));
// TODO: Turn on whenever ready to support encrypt-then-mac
var mac = false ? ComputeMac(encryptedBytes, iv) : null;
return new CipherString(Convert.ToBase64String(iv), Convert.ToBase64String(encryptedBytes), mac);
}
public string Decrypt(CipherString encyptedValue)
@ -141,9 +148,17 @@ namespace Bit.App.Services
throw new ArgumentNullException(nameof(encyptedValue));
}
if(encyptedValue.Mac != null)
{
var computedMac = ComputeMac(encyptedValue.CipherTextBytes, encyptedValue.InitializationVectorBytes);
if(computedMac != encyptedValue.Mac)
{
throw new InvalidOperationException("MAC failed.");
}
}
var provider = WinRTCrypto.SymmetricKeyAlgorithmProvider.OpenAlgorithm(SymmetricAlgorithm.AesCbcPkcs7);
var cryptoKey = provider.CreateSymmetricKey(Key);
var cryptoKey = provider.CreateSymmetricKey(encyptedValue.Mac != null ? MacKey : Key);
var decryptedBytes = WinRTCrypto.CryptographicEngine.Decrypt(cryptoKey, encyptedValue.CipherTextBytes,
encyptedValue.InitializationVectorBytes);
return Encoding.UTF8.GetString(decryptedBytes, 0, decryptedBytes.Length).TrimEnd('\0');
@ -155,6 +170,30 @@ namespace Bit.App.Services
}
}
private string ComputeMac(byte[] ctBytes, byte[] ivBytes)
{
if(MacKey == null)
{
throw new ArgumentNullException(nameof(MacKey));
}
if(ctBytes == null)
{
throw new ArgumentNullException(nameof(ctBytes));
}
if(ivBytes == null)
{
throw new ArgumentNullException(nameof(ivBytes));
}
var algorithm = WinRTCrypto.MacAlgorithmProvider.OpenAlgorithm(MacAlgorithm.HmacSha256);
var hasher = algorithm.CreateHash(MacKey);
hasher.Append(ivBytes.Concat(ctBytes).ToArray());
var mac = hasher.GetValueAndReset();
return Convert.ToBase64String(mac);
}
public byte[] MakeKeyFromPassword(string password, string salt)
{
if(password == null)