SymmetricDecrypt

Description

Decrypts a blob value using symmetric algorithm.

Applies to

CrypterObject objects

Syntax

crypter.SymmetricDecrypt ( algorithm, variable, key{, operationmode{, iv{, padding}}})

Argument	Description
crypter	The name of the CrypterObject object.
algorithm	A value of the SymmetricAlgorithm enumerated type that specifies the type of symmetric algorithm. Values are: AES! – The Advanced Encryption Standard DES! – The Data Encryption Standard TDES! – The Triple-DES DESX! – The DES-XEX3 Blowfish! – The Blowfish
variable	A blob whose value is the data you want to decrypt with symmetric algorithm. When using the system blob function to convert a string to a blob, it is recommended to specify its encoding argument to be EncodingANSI! (for English characters only) or EncodingUTF8!, otherwise, the default EncodingUTF16LE! will be used.
key	A blob specifying the secret key. The length of the secret key can be 128 bits, 192 bits, 256 bits with AES. The length of the secret key must be 64 bits with DES. The length of the secret key can be 128 bits, 192 bits with TDES. The length of the secret key must be 192 bits with DESX. The length of the secret key can be 32 bits~448 bits with Blowfish.
operationmode (optional)	A value of the OperationMode enumerated type that specifies the mode of operation. Values are: OperationModeECB! – (Default) The Electronic Codebook (ECB) mode OperationModeCBC! – The Cipher Block Chaining (CBC) mode OperationModeCFB! – The Cipher Feedback (CFB) mode OperationModeOFB! – The Output Feedback (OFB) mode OperationModeCTR! – The Counter (CTR) mode
iv (optional)	A blob specifying the initialization vector. Zeros filled by default. In the AES algorithm, the effective length of the iv is 16 bytes and the others are 8 bytes. If the length is not enough, it will be automatically filled with zeros. In the ECB operation mode, the iv will be ignored.
padding (optional)	A value of the PaddingScheme enumerated type that specifies the padding schemes used for block cipher. Values are: NoPadding! – No padding added to a block ZerosPadding! – 0's padding added to a block PKCSPadding! – PKCS #5 padding added to a block OneAndZerosPadding! – 1 and 0's padding added to a block DefaultPadding! – (Default) Default padding scheme. DefaultPadding! means PKCSPadding! for ECB or CBC mode. Otherwise, NoPadding! for modes like CFB, OFB, and CTR. ZerosPadding!, PKCSPadding!, and OneAndZerosPadding! can be used with ECB and CBC operation mode. NoPadding! can be used with CFB, OFB and CTR operation mode.

Return value

Blob.

Returns the result of the decrypt if it succeeds. If any argument's value is null, the method returns null. If an error occurs, throw the exception.

Examples

The following statements encrypt the data using AES and then decrypt the data using AES.

Blob lblb_data
Blob lblb_key
Blob lblb_iv
Blob lblb_encrypt
Blob lblb_decrypt

lblb_data = Blob("Test AES", EncodingANSI!)
lblb_key = Blob("Test Key12345678", EncodingANSI!)
lblb_iv = Blob("Test IV 12345678", EncodingANSI!)

CrypterObject lnv_CrypterObject
lnv_CrypterObject = Create CrypterObject

// Encrypt data using AES
lblb_encrypt = lnv_CrypterObject.SymmetricEncrypt(AES!, lblb_data, lblb_key, &
	OperationModeCBC!, lblb_iv, PKCSPadding!)

// Decrypt data using AES
lblb_decrypt = lnv_CrypterObject.SymmetricDecrypt(AES!, lblb_encrypt, lblb_key, &
	OperationModeCBC!, lblb_iv, PKCSPadding!)

messagebox("SymmetricDecrypt", string(lblb_decrypt, EncodingANSI!))

See also

AsymmetricGenerateKey

MD5

SHA

HMAC