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

, 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 PIN code, a password, a passphrase, a b ...

which was previously shared between the two parties using some

secure channel In cryptography, a secure channel is a means of data transmission that is resistant to overhearing and tampering. A confidential channel is a means of data transmission that is resistant to overhearing, or eavesdropping (e.g., reading the conten ...

before it needs to be used.

Key

To build a key from shared secret, the

key derivation function In cryptography, a key derivation function (KDF) is a cryptographic algorithm that derives one or more secret keys from a secret value such as a master key, a password, or a passphrase using a pseudorandom function (which typically uses a cr ...

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 Wireless LAN, local area networking of devices and Internet access, allowing nearby digital devices to exchange data by ...

encryption such as

Wired Equivalent Privacy Wired Equivalent Privacy (WEP) is an obsolete, and insecure security algorithm for 802.11 wireless networks. It was introduced as part of the original IEEE 802.11 standard ratified in 1997. The intention was to provide a level of security and pr ...

(WEP),

Wi-Fi Protected Access Wi-Fi Protected Access (WPA) (Wireless Protected Access), Wi-Fi Protected Access 2 (WPA2), and Wi-Fi Protected Access 3 (WPA3) are the three security certification programs developed after 2000 by the Wi-Fi Alliance to secure wireless computer n ...

(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 device, computer networking, a wireless access point (WAP) (also just access point (AP)) is a networking hardware device that allows other Wi-Fi devices to connect to a wired network or wireless network. As a standalone ...

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, 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 password-protected services t ...

, 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 Hexadecimal (also known as base-16 or simply hex) is a Numeral system#Positional systems in detail, positional numeral system that represents numbers using a radix (base) of sixteen. Unlike the decimal system representing numbers using ten symbo ...

string. The secret is used by all systems involved in the cryptographic processes used to secure the traffic between the systems.

Crypto system In cryptography, a cryptosystem is a suite of cryptographic algorithms needed to implement a particular security service, such as confidentiality (encryption). Typically, a cryptosystem consists of three algorithms: one for key generation, one fo ...

s 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 any practical brute force attack, though not in principle if an attacker has sufficient computational power (see password strength and password cracking 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 definite pattern or predictability in information. A random sequence of events, symbols or steps often has no order and does not follow an intelligible pattern or combination. ...

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 referred t ...

(CSPRNG) should be avoided.

References

{{Cryptography navbox Password authentication Key management

Key

See also

References