3.5 Symmetric encryption and decryption

The following predicates provide symmetric encryption and decryption:

evp_decrypt(+CipherText, +Algorithm, +Key, +IV, -PlainText, +Options)

Decrypt the given CipherText, using the symmetric algorithm Algorithm, key Key, and iv IV, to give PlainText. CipherText, Key and IV should all be strings, and PlainText is created as a string as well. Algorithm should be an algorithm which your copy of OpenSSL knows about. Examples are:

• aes-128-cbc
• aes-256-cbc
• des3

If the IV is not needed for your decryption algorithm (such as aes-128-ecb) then any string can be provided as it will be ignored by the underlying implementation

Options:

encoding(+Encoding)

Encoding to use for Data. Default is utf8. Alternatives are utf8 and octet.

padding(+PaddingScheme)

Padding scheme to use. Default is block. You can disable padding by supplying none here.

Example of aes-128-cbc encryption:

?- evp_encrypt("this is some input", 'aes-128-cbc', "sixteenbyteofkey",
               "sixteenbytesofiv", CipherText, []),
   evp_decrypt(CipherText, 'aes-128-cbc',
               "sixteenbyteofkey", "sixteenbytesofiv",
               RecoveredText, []).
CipherText = <binary string>
RecoveredText = "this is some input".

evp_encrypt(+PlainText, +Algorithm, +Key, +IV, -CipherTExt, +Options)

Encrypt the given PlainText, using the symmetric algorithm Algorithm, key Key, and iv IV, to give CipherText. See evp_decrypt/6.