decrypt
Type
command
Summary
Decrypt data using a cipher
Syntax
decrypt <source> using <cipher> with {password|key} <passorkey> [and salt <saltvalue>] [and IV <IVvalue>] [at <bitvalue> bit]
Description
The encrypt and decrypt commands accept the source data that will be encrypted or decrypted. The cipher is the name of the cipher obtained using the ciphernames function. The passorkey specifies the password or key that will be use for encryption or decryption as determined by the keyword before it. If you specify key then the key needs to be the same size (in bits, eight per byte) as the specified cipher key length. The key may optionally be accompanied by the IVvalue used by some ciphers. If you specify password or don't specify a key mode, then a password, typically text, will be used. The password may optionally be accompanied by a saltvalue. The bits specifies the key length in bits (for example, 64, 128, 192 or 256) and may be zero or empty for the default length (that is listed with the cipherNames function). Some ciphers have fixed key lengths and using an unsupported value will result in an error.
The key and IV value are the fundamental determiner in block ciphers. The IV value is typically the width (in bits) of the block associated with the cipher. The default value is zero. Its use is beyond the scope of this documentation.
The password and salt value are combined and scrambled to form the key and IV which are used as described above. The key derivation process is the same as that used in the openSSL utility. A 16-byte salt prefix is prepended to the encrypted data, based on the salt value. This is used in decryption. If no salt value is specified for a password, one is randomly generated. The use of a randomized salt value is a protection against dictionary attacks.
Some modes of block ciphers will pad data to be a multiple of block size. The padding method is that used by the openSSL utility and is a minimum of one byte.
The decrypt command is part of the SSL & Encryption library. To ensure that the command works in a standalone application, you must include this custom library when you create your standalone. In the Inclusions pane of the Standalone Application Settings window, make sure the "SSL & Encryption" library checkbox is checked.
Parameters
| Name | Type | Description |
|---|---|---|
source | the source input data | |
cipher | the format used to decrypt the data | |
passorkey | a password or key provided to the decryption routine, as necessary | |
saltvalue | the password may also be accompanied by a salt value | |
IVvalue | an IV (initialization vector) value may be specified for some cipher methods | |
bitvalue | the bit value specifies the key length in bits (ie. 64, 128, 192, 256, etc) |
Examples
-- the following copies a file from disk, stores it in a variable (myData), decrypts the result, then copies the file back to disk.
local path2input, myData, path2ouput
-- put the file path to your input and output files into path2input and path2output
put URL ("binfile:" & path2input) into myData
decrypt myData using "aes-256-cbc" with password "@&^2fy"
put it into URL("binfile:" & path2output)
Related
command: encrypt
function: cipherNames
glossary: Standalone Application Settings, command, LiveCode custom library
library: SSL & Encryption library
property: sslcertificates
Compatibility and Support
Introduced
LiveCode 2.5
OS
mac
windows
linux
ios
android
Platforms
desktop
server
mobile