hashcat/deps/yescrypt-master/COMPARISON

	Comparison of yescrypt to scrypt and Argon2.

yescrypt's advantages:

 + Greater resistance to offline attacks (increasing attacker's cost at
   same defender's cost)

   + yescrypt supports optional ROM for protection from use of botnet
     nodes (and other relatively small memory devices)

   + yescrypt has a dependency not only on RAM and maybe ROM, but
     also on fast on-die local memory (such as a CPU's L1 or L2 cache),
     which provides bcrypt-like anti-GPU properties even at very low
     per-hash RAM sizes (where scrypt and Argon2 are more likely to lose
     to bcrypt in terms of GPU attack speed) and even without ROM

   + yescrypt and scrypt currently have little low-level
     parallelism within processing of a block (yescrypt allows for
     tuning this later, scrypt does not), whereas Argon2 has a fixed and
     currently commonly excessive amount of such parallelism, which may
     be extracted to speed up e.g. GPU attacks through use of more
     computing resources per the same total memory size due to each hash
     computation's memory needs being split between 32 threads (yescrypt
     currently has four 16-byte lanes that can be processed in parallel
     within a 64-byte sub-block before running into a data dependency
     for the next sub-block, whereas Argon2 allows for parallel
     processing of eight 128-byte chunks within a 1 KiB block with only
     two synchronization points for the entire block, as well as of four
     32-byte parts of the 128-byte chunks with only two more
     synchronization points for the entire 1 KiB block)

   + yescrypt uses computation latency hardening based on integer
     multiplication and local memory access speed, which ties its
     per-hash RAMs up for a guaranteed minimum amount of time regardless
     of possibly much higher memory bandwidth on the attacker's
     hardware, whereas Argon2 uses only the multiplications and performs
     6 times fewer of those sequentially (96 sequential multiplications
     per 1 KiB for yescrypt vs. 16 per 1 KiB for Argon2, providing
     correspondingly different minimum time guarantees) and scrypt does
     not use this technique at all (but is no worse than Argon2 in this
     respect anyway due to having less low-level parallelism)

   + yescrypt and Argon2 are time-memory trade-off (TMTO) resistant
     (thus, computing them in less memory takes disproportionately
     longer), whereas scrypt is deliberately TMTO-friendly (and
     moreover, computing it in less memory takes up to 4x less than
     proportionately longer)

 + Extra optional built-in features

   + Hash encryption so that the hashes are not crackable without
     the key (to be stored separately)

   + Hash upgrade to higher settings without knowledge of password
     (temporarily removed from 1.0, to be re-added later)

   + SCRAM-like client-side computation of challenge responses
     (already part of the algorithm, not yet exposed via the API)

   + yescrypt's and Argon2's running time is tunable on top of
     memory usage and parallelism, unlike in scrypt's

 + Cryptographic security provided by NIST-approved primitives

   + (ye)scrypt's cryptographic security is provided by SHA-256,
     HMAC, and PBKDF2, which are NIST-approved and time-tested (the rest
     of yescrypt's processing, while most crucial for its offline attack
     resistance properties, provably does not affect its basic
     cryptographic hash properties), whereas Argon2 relies on the newer
     BLAKE2 (either choice is just fine for security, but use of
     approved algorithms may sometimes be required for compliance)

 + SHA-256, HMAC, PBKDF2, and scrypt are usable from the same codebase

yescrypt's drawbacks:

 - Complex (higher risk of human error occurring and remaining
   unnoticed for long)

 - Cache-timing unsafe (like bcrypt, scrypt, and Argon2d, but
   unlike Argon2i)

 - Not the PHC winner (Argon2 is), but is merely a "special recognition"

 - Supported in fewer third-party projects (as of this writing, there's
   yescrypt support in libxcrypt, Linux-PAM, shadow, and mkpasswd)

Other observations:

 * yescrypt's complexity is related to its current primary target use
   case (mass user authentication) and is relatively small compared to
   the total complexity of the authentication service, so the risk may
   be justified

 * Cache-timing safety is unimportant on dedicated servers, is
   mitigated for some use cases and threat models by proper use of
   salts, and is fully achieved in Argon2 only in its 2i flavor and only
   through reduction of resistance to the usual offline attacks compared
   to the 2d flavor

 * yescrypt's single-threaded memory filling speed on an otherwise
   idle machine and at our currently recommended settings is lower than
   Argon2's, but that's a result of our deliberate tuning (there's a
   knob to change that, but we don't recommend doing so) preventing
   yescrypt from bumping into memory access speed prematurely, and is
   irrelevant for determining server request rate capacity and maximum
   response latency where multiple instances or threads would be run
   (under that scenario, the algorithms deliver similar speeds)

 * yescrypt has been designed and currently configured to fit the
   SSE2 and NEON instruction sets and 128-bit SIMD perfectly, not
   benefiting from AVX's 3-register instructions (unlike classic scrypt,
   which doesn't fit SSE2 as perfectly and thus benefits from AVX and
   XOP) nor from AVX2's and AVX-512's wider SIMD (although it can be
   reconfigured for wider SIMD later), whereas Argon2 significantly
   benefits from those at least when running fewer threads or concurrent
   instances than are supported by the hardware (yet yescrypt's SSE2
   code is competitive with Argon2's AVX2 code under full server load)

 * yescrypt vs. Argon2 benchmarks are further complicated by these
   two schemes having different minimum amount of processing over memory
   (yescrypt's is 4/3 of Argon2's), and thus different average memory
   usage (5/8 of peak for yescrypt t=0 vs. 1/2 of peak for Argon2 t=1),
   which needs to be taken into account

 * scrypt benchmarks are also different in amount of processing over
   memory (twice Argon2's minimum) and average memory usage (3/4 of
   peak), but that's even further complicated by scrypt's
   TMTO-friendliness providing up to a 4x advantage to some attackers