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In cryptography, key size or key length refers to the number of bits in a key used by a cryptographic algorithm (such as a cipher).. Key length defines the upper-bound on an algorithm's security (i.e. a logarithmic measure of the fastest known attack against an algorithm), because the security of all algorithms can be violated by brute-force attacks.
The key size used for an AES cipher specifies the number of transformation rounds that convert the input, called the plaintext, into the final output, called the ciphertext. The number of rounds are as follows: 10 rounds for 128-bit keys. 12 rounds for 192-bit keys. 14 rounds for 256-bit keys.
256 bits is a common key size for symmetric ciphers in cryptography, such as Advanced Encryption Standard (AES). Increasing the word size can accelerate multiple precision mathematical libraries. Applications include cryptography .
AES key schedule for a 128-bit key. Define: N as the length of the key in 32-bit words: 4 words for AES-128, 6 words for AES-192, and 8 words for AES-256; K 0, K 1, ... K N-1 as the 32-bit words of the original key; R as the number of round keys needed: 11 round keys for AES-128, 13 keys for AES-192, and 15 keys for AES-256 [note 4] W 0, W 1, ...
SHA-2: A family of two similar hash functions, with different block sizes, known as SHA-256 and SHA-512. They differ in the word size; SHA-256 uses 32-bit words where SHA-512 uses 64-bit words. There are also truncated versions of each standard, known as SHA-224, SHA-384, SHA-512/224 and SHA-512/256. These were also designed by the NSA.
As of October 2012, CNSSP-15 [4] stated that the 256-bit elliptic curve (specified in FIPS 186-2), SHA-256, and AES with 128-bit keys are sufficient for protecting classified information up to the Secret level, while the 384-bit elliptic curve (specified in FIPS 186-2), SHA-384, and AES with 256-bit keys are necessary for the protection of Top ...
Using a 512-bit key would increase the cracking time to approaching 10 72 years, without increasing the time for encryption by more than a constant factor (depending on the encryption algorithms used). The limit has been further analysed in later literature as the maximum rate at which a system with energy spread can evolve into an orthogonal ...
SHA-2 (Secure Hash Algorithm 2) is a set of cryptographic hash functions designed by the United States National Security Agency (NSA) and first published in 2001. [3] [4] They are built using the Merkle–Damgård construction, from a one-way compression function itself built using the Davies–Meyer structure from a specialized block cipher.