cryptography Cryptography, or cryptology (from grc, , translit=kryptós "hidden, secret"; and ''graphein'', "to write", or ''-logia'', "study", respectively), is the practice and study of techniques for secure communication in the presence of adve ...

, a pre-shared key (PSK) is a

shared secret In cryptography, a shared secret is a piece of data, known only to the parties involved, in a secure communication. This usually refers to the key of a symmetric cryptosystem. The shared secret can be a password, a passphrase, a big number, o ...

which was previously shared between the two parties using some secure channel before it needs to be used.

Key

To build a key from shared secret, the key derivation function is typically used. Such systems almost always use symmetric key cryptographic algorithms. The term PSK is used in

Wi-Fi Wi-Fi () is a family of wireless network protocols, based on the IEEE 802.11 family of standards, which are commonly used for local area networking of devices and Internet access, allowing nearby digital devices to exchange data by radio w ...

encryption such as

Wired Equivalent Privacy Wired Equivalent Privacy (WEP) was a security algorithm for 802.11 wireless networks. Introduced as part of the original IEEE 802.11 standard ratified in 1997, its intention was to provide data confidentiality comparable to that of a traditional ...

(WEP),

Wi-Fi Protected Access Wi-Fi Protected Access (WPA), Wi-Fi Protected Access II (WPA2), and Wi-Fi Protected Access 3 (WPA3) are the three security and security certification programs developed after 2000 by the Wi-Fi Alliance to secure wireless computer networks. The Al ...

(WPA), where the method is called WPA-PSK or WPA2-PSK, and also in the Extensible Authentication Protocol (EAP), where it is known as EAP-PSK. In all these cases, both the

wireless access point In computer networking, a wireless access point (WAP), or more generally just access point (AP), is a networking hardware device that allows other Wi-Fi devices to connect to a wired network. As a standalone device, the AP may have a wired co ...

s (AP) and all clients ''share'' the same key. The characteristics of this secret or key are determined by the system which uses it; some system designs require that such keys be in a particular format. It can be a

password A password, sometimes called a passcode (for example in Apple devices), is secret data, typically a string of characters, usually used to confirm a user's identity. Traditionally, passwords were expected to be memorized, but the large number of ...

, a

passphrase A passphrase is a sequence of words or other text used to control access to a computer system, program or data. It is similar to a password in usage, but a passphrase is generally longer for added security. Passphrases are often used to control ...

, or a

hexadecimal In mathematics and computing, the hexadecimal (also base-16 or simply hex) numeral system is a positional numeral system that represents numbers using a radix (base) of 16. Unlike the decimal system representing numbers using 10 symbols, h ...

string. The secret is used by all systems involved in the cryptographic processes used to secure the traffic between the systems. Crypto systems rely on one or more keys for confidentiality. One particular attack is always possible against keys, the brute force key space search attack. A sufficiently long, randomly chosen, key can

resist A resist, used in many areas of manufacturing and art, is something that is added to parts of an object to create a pattern by protecting these parts from being affected by a subsequent stage in the process. Often the resist is then removed. For ...

any practical brute force attack, though not in principle if an attacker has sufficient computational power (see

password strength Password strength is a measure of the effectiveness of a password against guessing or brute-force attacks. In its usual form, it estimates how many trials an attacker who does not have direct access to the password would need, on average, to gu ...

and

password cracking In cryptanalysis and computer security, password cracking is the process of recovering passwords from data that has been stored in or transmitted by a computer system in scrambled form. A common approach ( brute-force attack) is to repeatedly t ...

for more discussion). Unavoidably, however, pre-shared keys are held by both parties to the communication, and so can be compromised at one end, without the knowledge of anyone at the other. There are several tools available to help one choose strong passwords, though doing so over any network connection is inherently unsafe as one cannot in general know who, if anyone, may be eavesdropping on the interaction. Choosing keys used by cryptographic algorithms is somewhat different in that any pattern whatsoever should be avoided, as any such pattern may provide an attacker with a lower effort attack than brute force search. This implies

random In common usage, randomness is the apparent or actual lack of pattern or predictability in events. A random sequence of events, symbols or steps often has no order and does not follow an intelligible pattern or combination. Individual rando ...

key choice to force attackers to spend as much effort as possible; this is very difficult in principle and in practice as well. As a general rule, any software except a

cryptographically secure pseudorandom number generator A cryptographically secure pseudorandom number generator (CSPRNG) or cryptographic pseudorandom number generator (CPRNG) is a pseudorandom number generator (PRNG) with properties that make it suitable for use in cryptography. It is also loosely kno ...

(CSPRNG) should be avoided.

References

{{Cryptography navbox Password authentication Authentication methods Key management

Key

See also

References