vely:decrypt-data

decrypt-data

Purpose: Decrypt data.

decrypt-data <data> to [ define ] <result> \
    [ input-length <input length> ] \
    [ output-length [ define ] <output length> ] \
    [ binary [ <binary> ] ] \
    ( password <password> \
        [ salt <salt> [ salt-length <salt length> ] ] \
        [ iterations <iterations> ] \
        [ cipher <cipher algorithm> ] \
        [ digest <digest algorithm> ]
        [ cache ]
        [ clear-cache <clear cache> ) \
    [ init-vector <init vector> ]

decrypt-data will decrypt <data> which must have been encrypted with encrypt-data, or other software using the same algorithms and clauses as specified.

If "input-length" clause is not used, the data to decrypt is considered to be a string, i.e. null-terminated, otherwise, if specified, then exactly <input length> bytes are decrypted. Password used for decryption is <password> (in "password" clause) and it must match the password used in encrypt-data. If "salt" clause is used, then string <salt> must match the salt used in encryption. If "init-vector" clause is used, then string <init vector> must match the IV (initialization vector) used in encryption. If "iterations" clause is used, then <iterations> must match the number used in encryption.

"output-length" clause lets you obtain the number of bytes in decrypted data in <output length>, which can be created with optional "define". The result of decryption is in <result> (in "to" clause) and can be created with optional "define". <result> is allocated memory.

If data was encrypted in binary mode (see encrypt-data), you must decrypt it with the same, and if it wasn't, then you must not use it in decrypt-data either. The reason for this is obvious - binary mode of encryption is encrypted data in its shortest form, and character mode (without "binary" or if <binary> evaluates to false) is the same data converted to a hexadecimal string - thus decryption must first convert such data back to binary before decrypting.

The cipher and digest algorithms (if specified as <cipher algorithm> and <digest algorithm> in "cipher" and "digest" clauses respectively) must match what was used in encrypt-data.

"cache" clause is used to cache the result of key computation, so it is not computed each time decryption takes place, while "clear-cache" allows key to be re-computed every time <clear cache> evaluates to boolean true. For more on "cache" and "clear-cache" clauses, as well as safety of encrypting/decrypting, see "Caching key" and "Safety" in encrypt-data.

Examples

See encrypt-data.