Encryption Algorithms can be categorized into different classifications:

• transformation type
• processing type
• cryptographic function type & number of keys used

Transformation Types

• substitution cipher - substituting every occurrence of a symbol/group-of-bits with another symbol/group-of-bits
• permutation/transposition cipher - rearranging a sequence of symbols/bits to some other pseudorandom sequence

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Processing Types

• block cipher is a method of encrypting text (to produce cipher-text) in which a cryptographic key and algorithm are applied to a block of data (for example, 64 contiguous bits) at once as a group rather than to one bit at a time
• stream cipher is a symmetric key cipher where plaintext digits are combined with a pseudorandom cipher digit stream (key-stream)

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Cryptographic Function Type & Number of Keys Used

Encryption Algorithms are classified in the following ways

Cryptographic Function Type	# of keys	description
Symmetric Key Function	1	both parties use same key to encrypt and decrypt all messages Link to original
Asymmetric Key Function	2	utilizes 2 distinct keys and is used for: encryption - the public-key (public encryption key) is used to encrypt messages, while the private-key (private decryption key) is used to decrypt signing - the private-key (private signing key) is used to sign a message which generates a digital signature, while the public-key (public signature key) is used to verify the message’s integrity Link to original
Keyed Cryptographic Hash Function	1	utilizes a cryptographic hash function and a secret cryptographic key for either: encryption - for message confidentiality HMAC - for message authenticity/integrity (HMAC is a hash-based form of MIC) secure hash functions generating HMACs could be used in place of “digital signatures”, but does not protect against non-repudiation (where 1 of the 2 parties that share the same key could secretly sign a message and say it was signed from the other) Link to original
PUF)	1	is a physically-defined “digital fingerprint” that serves as a unique identifier for a semiconductor device such as a microprocessor Link to original

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