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Hasty Pudding cipher
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Hasty Pudding cipher
The Hasty Pudding cipher (HPC) is a variable-block-size block cipher designed by Richard Schroeppel, which was an unsuccessful candidate in the competition for selecting the U.S. Advanced Encryption Standard (AES). It has a number of unusual properties for a block cipher: its input block size and key length are variable, and it includes an additional input parameter called the "spice" for use as a secondary, non-secret key. The Hasty Pudding cipher was the only AES candidate designed exclusively by U.S. cryptographers.
The Hasty Pudding cipher is in the public domain, and open source implementations are available.
The Hasty Pudding cipher consists of 5 different sub-ciphers:
The Hasty Pudding cipher algorithms all use 64-bit words internally. The cipher is designed to run on 64-bit machines, which can easily perform simple operations on 64-bit words.
The Hasty Pudding cipher can take a key of any number of bits for any one of the five subciphers. The cipher itself uses a key table of 16,384 bits (256 64-bit words). To derive the key table from the key, the key expansion function uses the following algorithm:
Each of the subciphers uses a different algorithm, but there are certain similarities. Three inputs are used to determine the ciphertext: the plaintext (in several 64-bit words plus one "fragment"), the spice (eight 64-bit words, with default value 0), and the key table. The operations within the cipher consist of stirring, which combines internal variables in various ways with values from the key table and spice at regular intervals. HPC-Short uses two fixed permutations in addition, and HPC-Tiny consists of many special sub-cases.
Decryption involves undoing the steps of encryption one by one. Many operations are easily undone (e.g. s0 = s0 + s1 is undone by computing s0 = s0 − s1). Other operations are more complex to undo. Some of the ideas involved include:
The Hasty Pudding cipher can also be used to encrypt values in a range that do not translate to strings with an integral number of bits; for instance, it can encrypt a number from 0 to N by producing another number from 0 to N. It does this by using the smallest subcipher that can handle the input as a bit string, and applying it to the input as a bit string, repeatedly, until the output is in the proper range.
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Hasty Pudding cipher
The Hasty Pudding cipher (HPC) is a variable-block-size block cipher designed by Richard Schroeppel, which was an unsuccessful candidate in the competition for selecting the U.S. Advanced Encryption Standard (AES). It has a number of unusual properties for a block cipher: its input block size and key length are variable, and it includes an additional input parameter called the "spice" for use as a secondary, non-secret key. The Hasty Pudding cipher was the only AES candidate designed exclusively by U.S. cryptographers.
The Hasty Pudding cipher is in the public domain, and open source implementations are available.
The Hasty Pudding cipher consists of 5 different sub-ciphers:
The Hasty Pudding cipher algorithms all use 64-bit words internally. The cipher is designed to run on 64-bit machines, which can easily perform simple operations on 64-bit words.
The Hasty Pudding cipher can take a key of any number of bits for any one of the five subciphers. The cipher itself uses a key table of 16,384 bits (256 64-bit words). To derive the key table from the key, the key expansion function uses the following algorithm:
Each of the subciphers uses a different algorithm, but there are certain similarities. Three inputs are used to determine the ciphertext: the plaintext (in several 64-bit words plus one "fragment"), the spice (eight 64-bit words, with default value 0), and the key table. The operations within the cipher consist of stirring, which combines internal variables in various ways with values from the key table and spice at regular intervals. HPC-Short uses two fixed permutations in addition, and HPC-Tiny consists of many special sub-cases.
Decryption involves undoing the steps of encryption one by one. Many operations are easily undone (e.g. s0 = s0 + s1 is undone by computing s0 = s0 − s1). Other operations are more complex to undo. Some of the ideas involved include:
The Hasty Pudding cipher can also be used to encrypt values in a range that do not translate to strings with an integral number of bits; for instance, it can encrypt a number from 0 to N by producing another number from 0 to N. It does this by using the smallest subcipher that can handle the input as a bit string, and applying it to the input as a bit string, repeatedly, until the output is in the proper range.