Root > Reference > All Functions > TwofishDeriveKey

Function TwofishDeriveKey

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Initializes Twofish key from password.

 

Unit

EEncrypt

 

Syntax

 

Code (Delphi)

function TwofishDeriveKey(

const APassword: String;

const ASalt: PSalt = nil

): TTwofishKey; overload;

 

function TwofishDeriveKey(

const AData: Pointer;

const ADataSize: Cardinal;

const ASalt: PSalt = nil

): TTwofishKey; overload;

 

Parameters

APassword [in, opt]

User password.

 

ASalt [in, opt]

Optional salt value. It is recommended to always use/specify salt when possible - to defend against dictionary and pre-computed rainbow table attacks. Use InitSalt function to create new salt for encryption and store salt with encrypted data. Use stored salt to decrypt data.

 

AData [in]

Pointer to binary password to initialize the key.

 

ADataSize [in]

Size of AData in bytes.

 

Return value

Precalculated 256-bit Twofish key derived from APassword and (optionally) ASalt.

 

Delete this key by using TwofishDestroyKey function.

 

This value is always the same for the same APassword (and same ASalt).

 

Important!

This is not RAW key derived from password. This is precalculated array of subkeys and SBox keys for Twofish cipher. Precalculation speed ups encryption/decryption. Use TwofishInitKey to precalculate key from RAW key.

 

Remarks

This function converts APassword to UTF-8, attaches ASalt (if specified), then uses the resulting RAW binary string to initialize the key. This function uses SHA-1 to derive key. Therefore the key has size of 256 bits.

 

Important!

The returned value of this function is not RAW key derived from password. The returned value is precalculated/cached array of subkeys and SBox keys for Twofish cipher. Precalculation speed ups encryption/decryption. Use TwofishInitKey to precalculate key from RAW key.

 

Delete the returned value by using TwofishDestroyKey function when you have finished working with key.

 

Overloaded variant lets you initialize key from any binary password.

 

Important!

Empty salt (zeroed) is not the same as no salt. Use TwofishInitSessionKey function to create new random salt. Once created, salt must be stored with encrypted data and then passed to TwofishDeriveKey for decryption.

 

Note

In cryptography, a salt is random data that is used as an additional input to a one-way function that hashes a password. The primary function of salts is to defend against dictionary attacks versus a list of password hashes and against pre-computed rainbow table attacks.

 

Twofish is a symmetric key block cipher with a block size of 128 bits and key sizes up to 256 bits. It was one of the five finalists of the Advanced Encryption Standard (AES) contest, but it was not selected for standardization. Twofish's distinctive features are the use of pre-computed key-dependent S-boxes, and a relatively complex key schedule. Twofish cipher has not been patented. As a result, the Twofish algorithm is free for anyone to use without any restrictions whatsoever. However, Twofish has seen less widespread usage than Blowfish, which has been available longer.

 

See also



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Last edited: 2018-11-26
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