The HKC authenticated stream cipher (Ver.1)

Authenticated encryption provides confidentiality and integrity in the same one-pass process, by computing a Message Authentication Code (MAC) at almost no cost over generating keystream. This is natively more efficient than providing confidentiality then authentication in separate passes. The argument as to whether compute MAC (on plaintext) then encrypt, encrypt then compute MAC (on ciphertext), or simultaneously encrypt and compute MAC (on plaintext, then encrypt plaintext and append MAC to ciphertext) was settled by Bellare and Namprempre [1] who showed that computing a MAC of the ciphertext best satisfies security properties of the typical scheme. HKC is a new stream cipher with a built in MAC routine that provides ‘encrypt then MAC’. HKC uses a 256-bit key to provide 256 bits of security. Its native environment is a processor that operates on 64-bit words, although it is also efficient in other environments. HKC is a family of Stream-Cipher-Based Authenticated Encryption algorithms. HKC’s heritage is the successful eSTREAM software portfolio cipher HC[2], designed by Hongjun Wu. HC is defined in two versions, respectively with 128and 256-bit keys, although only the former is included in the eSTREAM portfolio. HKC is based upon HC-256 to incorporate a MAC, to take advantage of larger register sizes on modern processors, and to remove or diminish what HKC’s authors perceive as inefficiencies.