Decrypt Method
Decrypts the payload.
procedure Decrypt();
Remarks
This method decrypts the input data.
Before calling the Decrypt method set InputMessage or InputFile to a valid compact serialized JWE string. For instance:
eyJhbGciOiJBMjU2R0NNS1ciLCJlbmMiOiJBMTI4Q0JDLUhTMjU2IiwiaXYiOiJMa0tNeTZ5Qlpfbzh6QW92IiwidGFnIjoiSmpMTkRsV3l3bWt3V2pMa0NLU0xxQSJ9.wiwySYm6fXZre-3IdT1tb_02KMQDrMICwUawVf7Gjhc.k84s7ne8J41QnA5BQ31k_A.kjIveRjjNYV4x92CVE9Agw.uAygkyeO2KWeFQIy9JLU0A
The type and format of the private key depends on the algorithm used to encrypt the data. The following table summarizes the relationship:
| Algorithm | Private Key Location |
| AES | Key |
| RSA and ECDH | Certificate |
| PBES | KeyPassword |
If this method returns without error decryption was successful. If decryption fails then this method raises an exception. After calling this method the payload will be present in the OutputMessage or file specified by OutputFile and the Header* properties will contain the headers. Headers of the parsed message are also available through the HeaderParam event.
The following properties are applicable when calling this method:
- Certificate (conditional - required for RSA and ECDH)
- Key (conditional - required for AES)
- ContentEncryptionAlgorithm (only if StrictValidation is True)
- EncryptionAlgorithm (only if StrictValidation is True)
- Header*
- Overwrite
- StrictValidation
Input and Output Properties
The component will determine the source and destination of the input and output based on which properties are set.
The order in which the input properties are checked is as follows:
When a valid source is found the search stops. The order in which the output properties are checked is as follows:
- SetOutputStream
- OutputFile
- OutputMessage: The output data is written to this property if no other destination is specified.
When using streams you may need to additionally set CloseInputStreamAfterProcessing or CloseOutputStreamAfterProcessing.
Notes for AES Algorithms (A128KW, A192KW, A256KW, A128GCMKW, A192GCMKW, A256GCMKW)
To decrypt messages that use AES encryption Key must be set to a key of appropriate length for the algorithm. For instance a 256 bit key would be used for A256KW.
The key must be known by both parties in order for encryption and decryption to take place.
byte[] key = new byte[] { 164, 60, 194, 0, 161, 189, 41, 38, 130, 89, 141, 164, 45, 170, 159, 209, 69, 137, 243, 216, 191, 131, 47, 250, 32, 107, 231, 117, 37, 158, 225, 234 };
Jwe jwe = new Jwe();
jwe.KeyB = key;
jwe.InputMessage = encryptedData;
jwe.Decrypt();
string decryptedData = jwe.OutputMessage;
Notes for RSA Algorithms (RSA1_5, RSA-OEAP, RSA-OAEP-256)
The RSA based algorithms use asymmetric encryption. Encrypting is done with a public key and decryption is done with a private key. The certificate with private key must be specified. For instance:
Jwe jwe = new Jwe();
jwe.Certificate = new Certificate(CertStoreTypes.cstPFXFile, "..\\jwt.pfx", "password", "*");
jwe.InputMessage = encryptedData;
jwe.Decrypt();
string decryptedData = jwe.OutputMessage;
Notes for ECDH Algorithms (ECDH-ES, ECDH-ES+A128KW, ECDH-ES+A192KW, ECDH-ES+A256KW)
ECDH algorithms require a valid ECC private key to decrypt the message. If the key was originally created with the ECC component the PEM encoded PrivateKey may be used directly with the Certificate property.
Jwe jwe = new Jwe();
jwe.Certificate = new Certificate(CertStoreTypes.cstPEMKeyFile, privKeyFile, "", "*");
jwe.InputMessage = encryptedData;
jwe.Decrypt();
string decryptedData = jwe.OutputMessage;
To use an ECC private key created by other means the ECC component may be used to import the key parameters. Populate the Rx, Ry, and KB properties of the ECC component first to obtain the PEM formatted public key. For instance:
Ecc ecc = new Ecc();
byte[] x_bytes = new byte[] { 171, 170, 196, 151, 94, 196, 231, 12, 128, 232, 17, 61, 45, 105, 41, 209, 192, 187, 112, 242, 110, 178, 95, 240, 36, 55, 83, 171, 190, 176, 78, 13 };
byte[] y_bytes = new byte[] { 197, 75, 134, 245, 245, 28, 199, 9, 7, 117, 1, 54, 49, 178, 135, 252, 62, 89, 35, 180, 117, 80, 231, 23, 110, 250, 28, 124, 219, 253, 224, 156 };
byte[] k_bytes = new byte[] { 81, 65, 201, 24, 235, 249, 162, 148, 169, 150, 109, 181, 61, 238, 145, 122, 31, 30, 151, 94, 239, 90, 222, 217, 63, 103, 54, 2, 176, 232, 248, 168 };
ecc.Key.RxB = x_bytes;
ecc.Key.RyB = y_bytes;
ecc.Key.KB = k_bytes;
string privKey = ecc.Key.PrivateKey;
Jwe jwe = new Jwe();
jwe.Certificate = new Certificate(CertStoreTypes.cstPEMKeyBlob, privKey, "", "*");
jwe.InputMessage = encryptedData;
jwe.Decrypt();
string decryptedData = jwe.OutputMessage;
Notes for PBES Algorithms (PBES2-HS256+A128KW, PBES2-HS384+A192KW, PBES2-HS512+A256KW
PBES algorithms derive a content encryption key from the KeyPassword property. Set KeyPassword to the shared secret.
Jwe jwe = new Jwe();
jwe.KeyPassword = "secret";
jwe.InputMessage = encryptedData;
jwe.Decrypt();
string decryptedData = jwe.OutputMessage;
Notes for Direct Shared Keys
When Direct encryption is used the Key property must be set to a valid symmetric key that will be used directly by the ContentEncryptionAlgorithm. For instance:
byte[] key = new byte[] { 164, 60, 194, 0, 161, 189, 41, 38, 130, 89, 141, 164, 45, 170, 159, 209, 69, 137, 243, 216, 191, 131, 47, 250, 32, 107, 231, 117, 37, 158, 225, 234 };
Jwe jwe = new Jwe();
jwe.KeyB = key;
jwe.InputMessage = encryptedData;
jwe.Decrypt();
string decryptedData = jwe.OutputMessage;