Salsa20

Updated 13 Aug 2026

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Definition
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  a modern stream cipher (from the eSTREAM project, concluded 2008) designed to be fast in both hardware and software, taking a 128- or 256-bit key plus a 64-bit Nonce
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How it works
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  expands (key, nonce, a block counter) into a 64-byte block via a fixed, invertible mixing function hh h applied 10 times, then adds the result word-by-word to the original input (since hh h alone is invertible and thus not random-looking on its own)
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  incrementing the counter across calls produces an arbitrarily long pseudorandom stream
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Performance
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  around 643 MB/s on a 2.2 GHz x86 machine in the original benchmarks — far faster than RC4 , and fast enough for real-time video encryption
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Status
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  no significant attacks known; one of several eSTREAM-selected modern alternatives to RC4/LFSR-based designs
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Related
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  Pseudorandom Generator (PRG)
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  Nonce

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