/// <summary>
/// Parses JWE token, extracts and unmarshal protected+unprotcted+per recipient headers
/// This method is NOT performing integrity checking and actual decryption
/// </summary>
/// <param name="jwe">Serialized JWE string to decrypt.</param>
/// <param name="settings">optional settings to override global DefaultSettings</param>
/// <returns>List of Jose headers. For Compact and Flattened this will be length 1 and contain just the protected header.
/// For General Json this will be the Jose headers (merge of protected, unprotected and per-recipient).</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 Headers(string jwe, JwtSettings settings = null)
{
settings = GetSettings(settings);
var token = JweToken.FromString(jwe, settings.JsonMapper);
var protectedHeader = settings.JsonMapper.Parse <IDictionary <string, object> >(
Encoding.UTF8.GetString(token.ProtectedHeaderBytes));
foreach (var recipient in token.Recipients)
{
try
{
recipient.JoseHeader = Dictionaries.MergeHeaders(protectedHeader, token.UnprotectedHeader, recipient.Header);
}
catch (ArgumentException)
{
throw new JoseException("Invalid JWE data, duplicate header keys found between protected, unprotected and recipient headers");
}
}
return(token);
}
/// <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));
}
}
