private static byte[] DecryptBytes(byte[][] parts, object key, JweAlgorithm?jweAlg, JweEncryption?jweEnc, JwtSettings settings = null)
{
byte[] header = parts[0];
byte[] encryptedCek = parts[1];
byte[] iv = parts[2];
byte[] cipherText = parts[3];
byte[] authTag = parts[4];
JwtSettings jwtSettings = GetSettings(settings);
IDictionary <string, object> jwtHeader = jwtSettings.JsonMapper.Parse <Dictionary <string, object> >(Encoding.UTF8.GetString(header));
JweAlgorithm headerAlg = jwtSettings.JwaAlgorithmFromHeader((string)jwtHeader["alg"]);
JweEncryption headerEnc = jwtSettings.JweAlgorithmFromHeader((string)jwtHeader["enc"]);
IKeyManagement keys = jwtSettings.Jwa(headerAlg);
IJweAlgorithm enc = jwtSettings.Jwe(headerEnc);
if (keys == null)
{
throw new JoseException(string.Format("Unsupported JWA algorithm requested: {0}", headerAlg));
}
if (enc == null)
{
throw new JoseException(string.Format("Unsupported JWE algorithm requested: {0}", headerEnc));
}
if (jweAlg != null && (JweAlgorithm)jweAlg != headerAlg)
{
throw new InvalidAlgorithmException("The algorithm type passed to the Decrypt method did not match the algorithm type in the header.");
}
if (jweEnc != null && (JweEncryption)jweEnc != headerEnc)
{
throw new InvalidAlgorithmException("The encryption type passed to the Decrypt method did not match the encryption type in the header.");
}
byte[] cek = keys.Unwrap(encryptedCek, key, enc.KeySize, jwtHeader);
byte[] aad = Encoding.UTF8.GetBytes(Compact.Serialize(header));
byte[] plainText = enc.Decrypt(aad, cek, iv, cipherText, authTag);
if (jwtHeader.ContainsKey("zip"))
{
var alg = (string)jwtHeader["zip"];
var compression = jwtSettings.Compression(GetJweCompression(alg));
if (compression == null)
{
throw new JoseException(string.Format("Unsupported compressions algorithm requested: {0}", alg));
}
plainText = compression.Decompress(plainText);
}
return(plainText);
}
/// <summary>
/// Decypts a JWE by performing necessary decompression/decryption and authenticated decryption as defined in RFC7516.
/// </summary>
/// <param name="jwe">JWE to decrypt.</param>
/// <param name="key">key for decoding suitable for JWE algorithm used to encrypt the CEK.</param>
/// <param name="expectedJweAlg">The algorithm type that we expect to receive in the header.</param>
/// <param name="expectedJweEnc">The encryption type that we expect to receive in the header.</param>
/// <param name="settings">optional settings to override global DefaultSettings</param>
/// <returns>Decrypted JweToken object</returns>
/// <exception cref="IntegrityException">if AEAD operation validation failed</exception>
/// <exception cref="EncryptionException">if JWE can't be decrypted</exception>
/// <exception cref="InvalidAlgorithmException">if encryption or compression algorithm is not supported</exception>
public static JweToken Decrypt(string jwe, object key, JweAlgorithm?expectedJweAlg = null, JweEncryption?expectedJweEnc = null, JwtSettings settings = null)
{
Ensure.IsNotEmpty(jwe, "Incoming jwe expected to be in a valid serialization form, not empty, whitespace or null.");
settings = GetSettings(settings);
JweToken token = Headers(jwe);
if (token.ProtectedHeaderBytes == null && token.Encoding == SerializationMode.Compact)
{
throw new JoseException(string.Format("Protected header was missing but required with compact encoding."));
}
var exceptions = new List <Exception>();
foreach (var recipient in token.Recipients)
{
var headerAlg = settings.JwaAlgorithmFromHeader((string)recipient.JoseHeader["alg"]);
var encryptedCek = recipient.EncryptedCek;
// skip recipient if asked to do strict validation
if (expectedJweAlg != null && expectedJweAlg != headerAlg)
{
continue;
}
IKeyManagement keys = settings.Jwa(headerAlg);
if (keys == null)
{
throw new JoseException(string.Format("Unsupported JWA algorithm requested: {0}", headerAlg));
}
try
{
JweEncryption headerEnc = settings.JweAlgorithmFromHeader((string)recipient.JoseHeader["enc"]);
IJweAlgorithm enc = settings.Jwe(headerEnc);
if (enc == null)
{
throw new JoseException(string.Format("Unsupported JWE algorithm requested: {0}", headerEnc));
}
if (expectedJweEnc != null && expectedJweEnc != headerEnc)
{
throw new InvalidAlgorithmException("The encryption type passed to the Decrypt method did not match the encryption type in the header.");
}
byte[] cek = keys.Unwrap(recipient.EncryptedCek, key, enc.KeySize, recipient.JoseHeader);
byte[] plaintext = enc.Decrypt(Aad(token.ProtectedHeaderBytes, token.Aad), cek, token.Iv, token.Ciphertext, token.AuthTag);
if (recipient.JoseHeader.TryGetValue("zip", out var compressionAlg))
{
var compression = settings.Compression((string)compressionAlg);
plaintext = compression.Decompress(plaintext);
}
token.PlaintextBytes = plaintext;
token.Recipient = recipient;
return(token);
}
catch (ArgumentException ex)
{
exceptions.Add(ex);
}
catch (JoseException ex)
{
exceptions.Add(ex);
}
}
// nobody was eligable for decryption
if (exceptions.Count == 0)
{
throw new InvalidAlgorithmException("The algorithm type passed to the Decrypt method did not match the algorithm type in the header.");
}
// decryption failed
if (exceptions.Select(e => new KeyValuePair <Type, String>(e.GetType(), e.Message)).Distinct().Count() == 1)
{
// throw the first
throw exceptions[0];
}
else
{
throw new JoseException($"No recipients able to decrypt.", new AggregateException(exceptions));
}
}
