bmx-site/docs/api/crypto/crypto_cipher.md

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id: crypto.cipher title: Crypto.Cipher

sidebar_label: Introduction

Supported Ciphers

Name	Block Size (bytes)	Key Range (bytes)	Rounds
Crypto.BlowfishCipher	8	8 ... 56	16
Crypto.TeaCipher	8	16	32
Crypto.XteaCipher	8	16	32
Crypto.AESCipher	16	16, 24, 32	10, 12, 14
Crypto.TwofishCipher	16	16, 24, 32	16
Crypto.DESCipher	8	8	16
3DES (EDE mode) (See Crypto.DESCipher)	8	16, 24	16
Crypto.Cast5Cipher	8	5 ... 16	12, 16
Crypto.NoekeonCipher	16	16	16
Crypto.SkipjackCipher	8	10	32
Crypto.AnubisCipher	16	16 ... 40	12 ... 18
Crypto.KhazadCipher	8	16	8
Crypto.KSEEDCipher	16	16	16
Crypto.KASUMICipher	8	16	8
Crypto.CamelliaCipher	16	16, 24, 32	18, 24
Crypto.IDEACipher	8	16	8
Crypto.SerpentCipher	16	16, 24, 32	32

Key sizes and Number of Rounds

As a general rule of thumb, do not use symmetric keys under 80 bits if you can help it. Only a few of the ciphers support smaller keys (mainly for test vectors anyways). Ideally, your application should be making at least 256 bit keys. This is not because you are to be paranoid. It is because if your PRNG has a bias of any sort the more bits the better. For example, if you have Pr[X = 1] = 1/2 ±γ where |γ| > 0 then the total amount of entropy in N bits is N·−log^2 (1/2 +|γ|). So if γ were 0.25 (a severe bias) a 256-bit string would have about 106 bits of entropy whereas a 128-bit string would have only 53 bits of entropy.

The number of rounds of most ciphers is not an option you can change. Only RC5 allows you to change the number of rounds. By passing zero as the number of rounds all ciphers will use their default number of rounds. Generally the ciphers are configured such that the default number of rounds provide adequate security for the given block and key size.

Types

Type	Description
TCipher	Cipher base type.
TCipherMode	Base type for cipher chaining modes.

Methods

Method BlockSize:Int() Abstract

The block size for this cipher.

Method Setup:Int(key:String, rounds:Int = 0) Abstract

Sets up the cipher to be used with a given number of rounds and a given key.

Method Setup:Int(key:Byte[], rounds:Int = 0) Abstract

Sets up the cipher to be used with a given number of rounds and a given key.

Method Setup:Int(key:Byte Ptr, keylen:Int, rounds:Int = 0) Abstract

Sets up the cipher to be used with a given number of rounds and a given key length.

Method Encrypt:Int(pt:Byte Ptr, ct:Byte Ptr) Abstract

Encrypts a single block of text, pt, storing the result in the ct buffer.

It is possible that the input and output buffer are the same buffer. The size of the block can be determined with BlockSize.

Method Decrypt:Int(ct:Byte Ptr, pt:Byte Ptr) Abstract

Decrypts a single block of text, ct, storing the result in the pt buffer.

It is possible that the input and output buffer are the same buffer. The size of the block can be determined with BlockSize.

Functions

Function GetCipher:TCipher(name:String)

Gets a cipher of the specified name.

A TNoSuchAlgorithmException is thrown if the requested cipher is not available.

Function GetBlockCipher:TBlockCipher(name:String)

Gets a block cipher of the specified name.

A TNoSuchAlgorithmException is thrown if the requested block cipher is not available.

Function GetStreamCipher:TStreamCipher(name:String)

Gets a stream cipher of the specified name.

A TNoSuchAlgorithmException is thrown if the requested stream cipher is not available.