public override ReadOnlySpan <byte> Decrypt(ReadOnlyMemory <byte> cipher, KerberosKey kerberosKey, KeyUsage usage)
{
var cipherLength = cipher.Length - ChecksumSize;
var Ke = kerberosKey.GetOrDeriveKey(
this,
$"{usage}|Ke|{KeySize}|{BlockSize}",
key => DK(key.Span, usage, KeyDerivationMode.Ke, KeySize, BlockSize).AsMemory()
);
var decrypted = AESCTS.Decrypt(
cipher.Span.Slice(0, cipherLength),
Ke,
AllZerosInitVector.Span
);
var actualChecksum = MakeChecksum(decrypted, kerberosKey, usage, KeyDerivationMode.Ki, ChecksumSize);
var expectedChecksum = cipher.Slice(cipherLength, ChecksumSize);
if (!AreEqualSlow(expectedChecksum.Span, actualChecksum))
{
throw new SecurityException("Invalid checksum");
}
return(decrypted.Slice(ConfounderSize, cipherLength - ConfounderSize));
}
public override ReadOnlyMemory <byte> Encrypt(ReadOnlyMemory <byte> data, KerberosKey kerberosKey, KeyUsage usage)
{
var Ke = kerberosKey.GetOrDeriveKey(
this,
$"{usage}|Ke|{KeySize}|{BlockSize}",
key => DK(key.Span, usage, KeyDerivationMode.Ke, KeySize, BlockSize)
);
var confounder = GenerateRandomBytes(ConfounderSize);
var concatLength = confounder.Length + data.Length;
using (var cleartextPool = CryptoPool.Rent <byte>(concatLength))
{
var cleartext = Concat(confounder.Span, data.Span, cleartextPool.Memory.Slice(0, concatLength));
var encrypted = AESCTS.Encrypt(
cleartext,
Ke.Span,
AllZerosInitVector.Span
);
var checksum = MakeChecksum(cleartext, kerberosKey, usage, KeyDerivationMode.Ki, ChecksumSize);
return(Concat(encrypted.Span, checksum.Span));
}
}
private ReadOnlyMemory <byte> GetOrDeriveKey(KerberosKey kerberosKey, KeyUsage usage)
{
return(kerberosKey.GetOrDeriveKey(
this,
$"{usage}|Ke|{KeySize}|{BlockSize}",
key => DK(key, usage, KeyDerivationMode.Ke, KeySize, BlockSize)
));
}
private ReadOnlyMemory <byte> GetOrDeriveKey(KerberosKey kerberosKey, KeyUsage usage)
{
if (kerberosKey == null)
{
throw new InvalidOperationException("Key cannot be null");
}
return(kerberosKey.GetOrDeriveKey(
this,
$"{usage}|Ke|{KeySize}|{BlockSize}",
key => DK(key, usage, KeyDerivationMode.Ke, KeySize, BlockSize)
));
}
public override ReadOnlyMemory <byte> MakeChecksum(
ReadOnlyMemory <byte> data,
KerberosKey key,
KeyUsage usage,
KeyDerivationMode kdf,
int hashSize
)
{
var ki = key.GetOrDeriveKey(
this,
$"{usage}|{kdf}|{KeySize}|{BlockSize}",
k => DK(k, usage, kdf, KeySize, BlockSize)
);
return(Hmac(ki, data).Slice(0, hashSize));
}
public override ReadOnlyMemory <byte> MakeChecksum(
ReadOnlyMemory <byte> data,
KerberosKey key,
KeyUsage usage,
KeyDerivationMode kdf,
int hashSize
)
{
if (key == null)
{
throw new ArgumentNullException(nameof(key));
}
var ki = key.GetOrDeriveKey(
this,
$"{usage}|{kdf}|{this.KeySize}|{this.BlockSize}",
k => DK(k, usage, kdf, this.KeySize, this.BlockSize)
);
return(Hmac(ki, data).Slice(0, hashSize));
}
public override ReadOnlyMemory <byte> Encrypt(ReadOnlyMemory <byte> data, KerberosKey kerberosKey, KeyUsage usage)
{
var Ke = kerberosKey.GetOrDeriveKey(
this,
$"{usage}|Ke|{KeySize}|{BlockSize}",
key => DK(key.Span, usage, KeyDerivationMode.Ke, KeySize, BlockSize).AsMemory()
);
var confounder = GenerateRandomBytes(ConfounderSize);
var cleartext = Concat(confounder.Span, data.Span);
var encrypted = AESCTS.Encrypt(
cleartext.Span,
Ke,
AllZerosInitVector.Span
);
var checksum = MakeChecksum(cleartext.Span, kerberosKey, usage, KeyDerivationMode.Ki, ChecksumSize);
return(Concat(encrypted, checksum));
}
