Public-key cryptography – Wikipedia, the free encyclopedia

Public-key cryptography, also known as asymmetric cryptography, is a class of cryptographic algorithms which requires two separate keys, one of which is secret (or private) and one of which is public. Although different, the two parts of this key pair are mathematically linked. The public key is used to encrypt plaintext or to verify a digital signature; whereas the private key is used to decrypt ciphertext or to create a digital signature. The term "asymmetric" stems from the use of different keys to perform these opposite functions, each the inverse of the other as contrasted with conventional ("symmetric") cryptography which relies on the same key to perform both.

Public-key algorithms are based on mathematical problems which currently admit no efficient solution that are inherent in certain integer factorization, discrete logarithm, and elliptic curve relationships. It is computationally easy for a user to generate their own public and private key-pair and to use them for encryption and decryption. The strength lies in the fact that it is "impossible" (computationally infeasible) for a properly generated private key to be determined from its corresponding public key. Thus the public key may be published without compromising security, whereas the private key must not be revealed to anyone not authorized to read messages or perform digital signatures. Public key algorithms, unlike symmetric key algorithms, do not require a secure initial exchange of one (or more) secret keys between the parties.

Message authentication involves processing a message with a private key to produce a digital signature. Thereafter anyone can verify this signature by processing the signature value with the signer's corresponding public key and comparing that result with the message. Success confirms the message is unmodified since it was signed, and presuming the signer's private key has remained secret to the signer that the signer, and no one else, intentionally performed the signature operation. In practice, typically only a hash or digest of the message, and not the message itself, is encrypted as the signature.

Public-key algorithms are fundamental security ingredients in cryptosystems, applications and protocols. They underpin various Internet standards, such as Transport Layer Security (TLS), S/MIME, PGP, and GPG. Some public key algorithms provide key distribution and secrecy (e.g., DiffieHellman key exchange), some provide digital signatures (e.g., Digital Signature Algorithm), and some provide both (e.g., RSA).

Public-key cryptography finds application in, amongst others, the IT security discipline information security. Information security (IS) is concerned with all aspects of protecting electronic information assets against security threats.[1] Public-key cryptography is used as a method of assuring the confidentiality, authenticity and non-repudiability of electronic communications and data storage.

Public-key cryptography is often used to secure electronic communication over an open networked environment such as the internet. Open networked environments are susceptible to a variety of communication security problems such as man-in-the-middle attacks and other security threats. Sending a secure communication means that the communication being sent must not be readable during transit (preserving confidentiality), the communication must not be modified during transit (preserving the integrity of the communication) and to enforce non-repudiation or non-denial of the sending of the communication. Combining public-key cryptography with an Enveloped Public Key Encryption (EPKE)[2] method, allows for the secure sending of a communication over an open networked environment.

The distinguishing technique used in public-key cryptography is the use of asymmetric key algorithms, where the key used to encrypt a message is not the same as the key used to decrypt it. Each user has a pair of cryptographic keys a public encryption key and a private decryption key. Similarly, a key pair used for digital signatures consists of a private signing key and a public verification key. The public key is widely distributed, while the private key is known only to its proprietor. The keys are related mathematically, but the parameters are chosen so that calculating the private key from the public key is either impossible or prohibitively expensive.

In contrast, symmetric-key algorithms variations of which have been used for thousands of years use a single secret key, which must be shared and kept private by both the sender and the receiver, for both encryption and decryption. To use a symmetric encryption scheme, the sender and receiver must securely share a key in advance.

Because symmetric key algorithms are nearly always much less computationally intensive than asymmetric ones, it is common to exchange a key using a key-exchange algorithm, then transmit data using that key and a symmetric key algorithm. PGP and the SSL/TLS family of schemes use this procedure, and are thus called hybrid cryptosystems.

There are two main uses for public-key cryptography:

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Public-key cryptography - Wikipedia, the free encyclopedia