해시는 임의의 길이를 갖는 임의의 데이터를 고정된 길이의 데이터로 매핑하는 단방향 함수를 말합니다.

그러나 오래된 해시함수의 경우 알고리즘의 취약점이 발견되면서 역으로 평문값을 알아낼 수 있는 경우도 존재합니다. 특히 각종 워게임에서 크랙이 가능한 취약한 해시 함수들을 많이 응용하고 있으며 실제로 취약한 해시를 사용하고 있는 서비스도 존재합니다.

해당 해시가 취약한 알고리즘으로 구성되어 있는지 검증하기 위해서는 해시값의 형태나 길이로 종류를 판단하고 크랙을 시도해야 합니다.

이때 참고할 수 있는 해시 알고리즘의 종류와 길이를 정리해 보았습니다.

순환 중복 검사(Cyclic Redundancy Checks)

Name	Length(str)	Length(bit)	Type
checksum (Unix)	8	32 bits	CRC with length appended
CRC-16	4	16 bits	CRC
CRC-32	8	32 bits	CRC
CRC-32 MPEG-2	8	32 bits	CRC
CRC-32C	8	32 bits	CRC
CRC-64	16	64 bits	CRC

Checksums

Name	Length(str)	Length(bit)	Type
BSD checksum (Unix)	4	16 bits	sum with circular rotation
SYSV checksum (Unix)	4	16 bits	sum with circular rotation
sum8	2	8 bits	sum
Internet Checksum	4	16 bits	sum (ones’ complement)
sum24	6	24 bits	sum
sum32	8	32 bits	sum
fletcher-4	1	4 bits	sum
fletcher-8	2	8 bits	sum
fletcher-16	4	16 bits	sum
fletcher-32	8	32 bits	sum
Adler-32	8	32 bits	sum
xor8	2	8 bits	sum
Luhn algorithm	1	1 decimal digit	sum
Verhoeff algorithm	1	1 decimal digit	sum
Damm algorithm	1	1 decimal digit	Quasigroup operation operation

Name	Length	Type
Rabin fingerprint	variable	multiply
tabulation hashing	variable	XOR
universal one-way hash function
Zobrist hashing	variable	XOR

Name	Length(str)	Length(bit)	Type
Pearson hashing	2	8 bits (or more)	XOR/table
Paul Hsieh’s SuperFastHash	8	32 bits
Buzhash		variable	XOR/table
Fowler-Noll-Vo hash function(FNV Hash)	8, 16, 32, 64, 128, or 256	32, 64, 128, 256,512, or 1024 bits	xor/product orproduct/XOR
Jenkins hash function	8 or 16	32 or 64 bits	XOR/addition
Bernstein’s hash djb2	8 or 16	32 or 64 bits	shift/add or mult/addor shift/add/xor or mult/xor
PJW hash / Elf Hash	8 or 16	32 or 64 bits	add,shift,xor
MurmurHash	8, 16, or 32	32, 64, or 128 bits	product/rotation
Fast-Hash	8, 16	32, 64 bits	xorshift
SpookyHash	8, 16, or 32	32, 64, or 128 bits	see Jenkins hash function
CityHash	8, 16, 32, or 64	32, 64, 128, or 256 bits
FarmHash	8, 16, or 32	32, 64 or 128 bits
MetroHash	16 or 32	64 or 128 bits
numeric hash (nhash)		variable	division/modulo
xxHash	8, 16, 32	32, 64, 128 bits	product/rotation
t1ha (Fast Positive Hash)	16 and 32	64 and 128 bits	product/rotation/XOR/add
pHash		fixed or variable	see Perceptual hashing
dhash	32	128 bits	see Perceptual hasing
SDBM	8 or 16	32 or 64 bits	mult/add or shift/addalso used in GNU AWK
OSDB hash	16	64 bits	add

Name	Tag Length	Type
BLAKE2	arbitrary	keyed hash function (prefix-MAC)
BLAKE3	arbitrary	keyed hash function (supplied IV)
HMAC
KMAC	arbitrary	based on Keccak
MD6	512 bits	Merkle tree NLFSR
One-key MAC (OMAC; CMAC)
PMAC (cryptography)
Poly1305-AES	128 bits	nonce-based
SipHash	32, 64 or 128 bits	non-collision-resistant PRF
HighwayHash	64, 128 or 256 bits	non-collision-resistant PRF
UMAC
VMAC

Name	Length(str)	Length(bit)	Type
BLAKE-256	64	256 bits	HAIFA structure
BLAKE-512	128	512 bits	HAIFA structure
BLAKE2s	up to 64	up to 256 bits	HAIFA structure
BLAKE2b	up to 128	up to 512 bits	HAIFA structure
BLAKE2X	arbitrary	arbitrary	HAIFA structure, extensible-output functions (XOFs) design
BLAKE3	arbitrary	arbitrary	Merkle tree
ECOH	56 to 128	224 to 512 bits	hash
FSB	40 to 128	160 to 512 bits	hash
GOST	64	256 bits	hash
Grøstl	up to 128	up to 512 bits	hash
HAS-160	40	160 bits	hash
HAVAL	32 to 64	128 to 256 bits	hash
JH	56 to 128	224 to 512 bits	hash
LSH	64 to 128	256 to 512 bits	wide-pipe Merkle–Damgård construction
MD2	32	128 bits	hash
MD4	32	128 bits	hash
MD5	32	128 bits	Merkle–Damgård construction
MD6	up to 128	up to 512 bits	Merkle tree NLFSR (it is also a keyed hash function)
RadioGatún	arbitrary	arbitrary	ideal mangling function
RIPEMD	32	128 bits	hash
RIPEMD-128	32	128 bits	hash
RIPEMD-160	40	160 bits	hash
RIPEMD-320	80	320 bits	hash
SHA-1	40	160 bits	Merkle–Damgård construction
SHA-224	56	224 bits	Merkle–Damgård construction
SHA-256	64	256 bits	Merkle–Damgård construction
SHA-384	96	384 bits	Merkle–Damgård construction
SHA-512	128	512 bits	Merkle–Damgård construction
SHA-3 (subset of Keccak)	arbitrary	arbitrary	sponge function
Skein	arbitrary	arbitrary	Unique Block Iteration
Snefru	32 or 64	128 or 256 bits	hash
Spectral Hash	128	512 bits	wide-pipe Merkle–Damgård construction
Streebog	64 or 128	256 or 512 bits	Merkle–Damgård construction
SWIFFT	128	512 bits	hash
Tiger	48	192 bits	Merkle–Damgård construction
Whirlpool	128	512 bits	hash