In cryptography, a key derivation function (or KDF) is a function which derives one or more secret keys from a secret value and/or other known information such as a password or passphrase. Kraft durch Freude ( KdF, literally "Strength through Joy" was a large state-controlled Leisure organization in the Third Reich, a part of the Cryptography (or cryptology; from Greek grc κρυπτός kryptos, "hidden secret" and grc γράφω gráphō, "I write" In Cryptography, a key is a piece of information (a Parameter) that determines the functional output of a cryptographic algorithm In computing a password is a Word or string of characters that is entered often along with a user name, in modern times usually into a computer system A passphrase is a sequence of words or other text used to control access to a computer system program or data Key derivation functions internally often use a cryptographic hash function. A cryptographic Hash function is a transformation that takes an input (or 'message' and returns a fixed-size string which is called the hash value (sometimes
Key derivation functions are often used in conjunction with non-secret parameters to derive one or more keys from a common secret value. Such use may prevent an attacker who obtains a derived key from learning useful information about either the input secret value or any of the other derived keys. A KDF may also be used to ensure that derived keys have other desirable properties, such as avoiding "weak keys" in some specific encryption systems.
Key derivation functions are often used as components of multi-party key-agreement protocols. In Cryptography, a key-agreement protocol is a protocol whereby two or more parties can agree on a key in such a way that both influence the outcome Examples of such key derivation functions include KDF1, defined in IEEE Std 1363-2000, and similar functions in ANSI X9. IEEE P1363 is an Institute of Electrical and Electronics Engineers (IEEE standardization project for Public-key cryptography. 42.
Key derivation functions are also used to derive keys from secret passwords or passphrases.
Key derivation functions are also used in applications to derive keys from secret passwords or passphrases, which typically do not have the desired properties to be used directly as cryptographic keys. In Cryptography, key strengthening or key stretching refer to techniques used to make a possibly-weak key, typically a Password or Passphrase In such applications, it is generally recommended that the key derivation function be made deliberately slow so as to frustrate brute-force attack or dictionary attack on the password or passphrase input value. In Cryptanalysis, a brute force attack is a method of defeating a Cryptographic scheme by trying a large number of possibilities for example possible keys In Cryptanalysis and Computer security, a dictionary attack is a technique for defeating a Cipher or authentication mechanism by trying to determine its
Such use may be expressed as DK = KDF(Key,Salt,Iterations) where DK is the derived key, KDF is the key derivation function, Key is the original key or password, Salt is a random number which acts as cryptographic salt, and Iterations refers to the number of iterations of a sub-function. In Computer science, a subroutine ( function, method, procedure, or subprogram) is a portion of code within a larger In Cryptography, a salt comprises random Bits that are used as one of the inputs to a Key derivation function. Iteration means the act of repeating Mathematics Iteration in mathematics may refer to the process of iterating a function, or to the techniques used The derived key is used instead of the original key or password as the key to the system. The values of the salt and the number of iterations (if it isn't fixed) are stored with the hashed password or sent as plaintext with an encrypted message.
The difficulty of a brute force attack increases with the number of iterations. In Cryptanalysis, a brute force attack is a method of defeating a Cryptographic scheme by trying a large number of possibilities for example possible keys A practical limit on the iteration count is the unwillingness of users to tolerate a perceptible delay in logging in to a computer or seeing a decrypted message. The use of salt prevents the attackers from precomputing a dictionary of derived keys. In Cryptography, a salt comprises random Bits that are used as one of the inputs to a Key derivation function.
The first deliberately-slow password-based key derivation function was called "crypt" (or "crypt(3)" after its man page), and was invented by Robert Morris in the 1980s to encrypt Unix passwords. Almost all substantial UNIX and Unix-like Operating systems have extensive documentation known as man pages (short for "manual pages" Robert "Bob" H Morris is an American Cryptographer. He received a Bachelor's degree in Mathematics from Harvard University Unix (officially trademarked as UNIX, sometimes also written as Unix with Small caps) is a computer While it was a great advance at the time, increases in processor speeds since the PDP-11 era have made brute-force attacks against crypt feasible, and advances in storage have rendered the 12-bit salt inadequate. The PDP-11 was a series of 16-bit Minicomputers sold by Digital Equipment Corp In Cryptanalysis, a brute force attack is a method of defeating a Cryptographic scheme by trying a large number of possibilities for example possible keys The crypt function's design also limits the user password to 8 characters, which limits the keyspace and makes strong passphrases impossible. A passphrase is a sequence of words or other text used to control access to a computer system program or data
Modern password-based key derivation functions, such as PBKDF2 (specified in RFC 2898), use a cryptographic hash, such as MD5 or SHA1, more salt (e. PBKDF2 (Password-Based Key Derivation Function is a Key derivation function that is part of RSA Laboratories ' Public-Key Cryptography Standards (PKCS series In Cryptography, MD5 ( Message-Digest algorithm 5) is a widely used partially insecure Cryptographic hash function with a 128- Bit hash value g. 64 bits) and a high iteration count (often 1000 or more). There have been proposals to use algorithms that require large amounts of computer memory and other computing resources to make custom hardware attacks more difficult to mount. In Cryptography, a custom hardware attack uses specially designed electronic circuits to decipher encrypted messages.