LSH (hash function)

LSH is a cryptographic hash function designed in 2014 by South Korea to provide integrity in general-purpose software environments such as PCs and smart devices.^[1] LSH is one of the cryptographic algorithms approved by the Korean Cryptographic Module Validation Program (KCMVP). And it is the national standard of South Korea (KS X 3262).

The overall structure of the hash function LSH is shown in the following figure.

The hash function LSH has the wide-pipe Merkle-Damgård structure with one-zeros padding. The message hashing process of LSH consists of the following three stages.

1. Initialization:
   • One-zeros padding of a given bit string message.
   • Conversion to 32-word array message blocks from the padded bit string message.
   • Initialization of a chaining variable with the initialization vector.
2. Compression:
   • Updating of chaining variables by iteration of a compression function with message blocks.
3. Finalization:
   • Generation of an ${\displaystyle n}$-bit hash value from the final chaining variable.

The specifications of the hash function LSH are as follows.

Hash function LSH specifications

Algorithm	Digest size in bits (${\displaystyle n}$)	Number of step functions (${\displaystyle N_{s}}$)	Chaining variable size in bits	Message block size in bits	Word size in bits (${\displaystyle w}$)
LSH-256-224	224	26	512	1024	32
LSH-256-256	256
LSH-512-224	224	28	1024	2048	64
LSH-512-256	256
LSH-512-384	384
LSH-512-512	512

Let ${\displaystyle m}$ be a given bit string message. The given ${\displaystyle m}$ is padded by one-zeros, i.e., the bit ‘1’ is appended to the end of ${\displaystyle m}$, and the bit ‘0’s are appended until a bit length of a padded message is ${\displaystyle 32wt}$, where ${\displaystyle t=\lceil (|m|+1)/32w\rceil }$ and ${\displaystyle \lceil x\rceil }$ is the smallest integer not less than ${\displaystyle x}$.

Let ${\displaystyle m_{p}=m_{0}\|m_{1}\|\ldots \|m_{(32wt-1)}}$ be the one-zeros-padded ${\displaystyle 32wt}$-bit string of ${\displaystyle m}$. Then ${\displaystyle m_{p}}$ is considered as a ${\displaystyle 4wt}$-byte array ${\displaystyle m_{a}=(m[0],\ldots ,m[4wt-1])}$, where ${\displaystyle m[k]=m_{8k}\|m_{(8k+1)}\|\ldots \|m_{(8k+7)}}$ for all ${\displaystyle 0\leq k\leq (4wt-1)}$. The ${\displaystyle 4wt}$-byte array ${\displaystyle m_{a}}$ converts into a ${\displaystyle 32t}$-word array ${\displaystyle {\textsf {M}}=(M[0],\ldots ,M[32t-1])}$ as follows.

${\displaystyle M[s]\leftarrow m[ws/8+(w/8-1)]\|\ldots \|m[ws/8+1]\|m[ws/8]}$ ${\displaystyle (0\leq s\leq (32t-1))}$

From the word array ${\displaystyle {\textsf {M}}}$, we define the ${\displaystyle t}$ 32-word array message blocks ${\displaystyle \{{\textsf {M}}^{(i)}\}_{i=0}^{t-1}}$ as follows.

${\displaystyle {\textsf {M}}^{(i)}\leftarrow (M[32i],M[32i+1],\ldots ,M[32i+31])}$ ${\displaystyle (0\leq i\leq (t-1))}$

The 16-word array chaining variable ${\displaystyle {\textsf {CV}}^{(0)}}$ is initialized to the initialization vector ${\displaystyle {\textsf {IV}}}$.

${\displaystyle {\textsf {CV}}^{(0)}[l]\leftarrow {\textsf {IV}}[l]}$ ${\displaystyle (0\leq l\leq 15)}$

The initialization vector ${\displaystyle {\textsf {IV}}}$ is as follows. In the following tables, all values are expressed in hexadecimal form.

LSH-256-224 initialization vector

${\displaystyle {\textsf {IV}}[0]}$	${\displaystyle {\textsf {IV}}[1]}$	${\displaystyle {\textsf {IV}}[2]}$	${\displaystyle {\textsf {IV}}[3]}$	${\displaystyle {\textsf {IV}}[4]}$	${\displaystyle {\textsf {IV}}[5]}$	${\displaystyle {\textsf {IV}}[6]}$	${\displaystyle {\textsf {IV}}[7]}$
068608D3	62D8F7A7	D76652AB	4C600A43	BDC40AA8	1ECA0B68	DA1A89BE	3147D354
${\displaystyle {\textsf {IV}}[8]}$	${\displaystyle {\textsf {IV}}[9]}$	${\displaystyle {\textsf {IV}}[10]}$	${\displaystyle {\textsf {IV}}[11]}$	${\displaystyle {\textsf {IV}}[12]}$	${\displaystyle {\textsf {IV}}[13]}$	${\displaystyle {\textsf {IV}}[14]}$	${\displaystyle {\textsf {IV}}[15]}$
707EB4F9	F65B3862	6B0B2ABE	56B8EC0A	CF237286	EE0D1727	33636595	8BB8D05F

LSH-256-256 initialization vector

${\displaystyle {\textsf {IV}}[0]}$	${\displaystyle {\textsf {IV}}[1]}$	${\displaystyle {\textsf {IV}}[2]}$	${\displaystyle {\textsf {IV}}[3]}$	${\displaystyle {\textsf {IV}}[4]}$	${\displaystyle {\textsf {IV}}[5]}$	${\displaystyle {\textsf {IV}}[6]}$	${\displaystyle {\textsf {IV}}[7]}$
46A10F1F	FDDCE486	B41443A8	198E6B9D	3304388D	B0F5A3C7	B36061C4	7ADBD553
${\displaystyle {\textsf {IV}}[8]}$	${\displaystyle {\textsf {IV}}[9]}$	${\displaystyle {\textsf {IV}}[10]}$	${\displaystyle {\textsf {IV}}[11]}$	${\displaystyle {\textsf {IV}}[12]}$	${\displaystyle {\textsf {IV}}[13]}$	${\displaystyle {\textsf {IV}}[14]}$	${\displaystyle {\textsf {IV}}[15]}$
105D5378	2F74DE54	5C2F2D95	F2553FBE	8051357A	138668C8	47AA4484	E01AFB41

LSH-512-224 initialization vector

${\displaystyle {\textsf {IV}}[0]}$	${\displaystyle {\textsf {IV}}[1]}$	${\displaystyle {\textsf {IV}}[2]}$	${\displaystyle {\textsf {IV}}[3]}$
0C401E9FE8813A55	4A5F446268FD3D35	FF13E452334F612A	F8227661037E354A
${\displaystyle {\textsf {IV}}[4]}$	${\displaystyle {\textsf {IV}}[5]}$	${\displaystyle {\textsf {IV}}[6]}$	${\displaystyle {\textsf {IV}}[7]}$
A5F223723C9CA29D	95D965A11AED3979	01E23835B9AB02CC	52D49CBAD5B30616
${\displaystyle {\textsf {IV}}[8]}$	${\displaystyle {\textsf {IV}}[9]}$	${\displaystyle {\textsf {IV}}[10]}$	${\displaystyle {\textsf {IV}}[11]}$
9E5C2027773F4ED3	66A5C8801925B701	22BBC85B4C6779D9	C13171A42C559C23
${\displaystyle {\textsf {IV}}[12]}$	${\displaystyle {\textsf {IV}}[13]}$	${\displaystyle {\textsf {IV}}[14]}$	${\displaystyle {\textsf {IV}}[15]}$
31E2B67D25BE3813	D522C4DEED8E4D83	A79F5509B43FBAFE	E00D2CD88B4B6C6A

LSH-512-256 initialization vector

${\displaystyle {\textsf {IV}}[0]}$	${\displaystyle {\textsf {IV}}[1]}$	${\displaystyle {\textsf {IV}}[2]}$	${\displaystyle {\textsf {IV}}[3]}$
6DC57C33DF989423	D8EA7F6E8342C199	76DF8356F8603AC4	40F1B44DE838223A
${\displaystyle {\textsf {IV}}[4]}$	${\displaystyle {\textsf {IV}}[5]}$	${\displaystyle {\textsf {IV}}[6]}$	${\displaystyle {\textsf {IV}}[7]}$
39FFE7CFC31484CD	39C4326CC5281548	8A2FF85A346045D8	FF202AA46DBDD61E
${\displaystyle {\textsf {IV}}[8]}$	${\displaystyle {\textsf {IV}}[9]}$	${\displaystyle {\textsf {IV}}[10]}$	${\displaystyle {\textsf {IV}}[11]}$
CF785B3CD5FCDB8B	1F0323B64A8150BF	FF75D972F29EA355	2E567F30BF1CA9E1
${\displaystyle {\textsf {IV}}[12]}$	${\displaystyle {\textsf {IV}}[13]}$	${\displaystyle {\textsf {IV}}[14]}$	${\displaystyle {\textsf {IV}}[15]}$
B596875BF8FF6DBA	FCCA39B089EF4615	ECFF4017D020B4B6	7E77384C772ED802

LSH-512-384 initialization vector

${\displaystyle {\textsf {IV}}[0]}$	${\displaystyle {\textsf {IV}}[1]}$	${\displaystyle {\textsf {IV}}[2]}$	${\displaystyle {\textsf {IV}}[3]}$
53156A66292808F6	B2C4F362B204C2BC	B84B7213BFA05C4E	976CEB7C1B299F73
${\displaystyle {\textsf {IV}}[4]}$	${\displaystyle {\textsf {IV}}[5]}$	${\displaystyle {\textsf {IV}}[6]}$	${\displaystyle {\textsf {IV}}[7]}$
DF0CC63C0570AE97	DA4441BAA486CE3F	6559F5D9B5F2ACC2	22DACF19B4B52A16
${\displaystyle {\textsf {IV}}[8]}$	${\displaystyle {\textsf {IV}}[9]}$	${\displaystyle {\textsf {IV}}[10]}$	${\displaystyle {\textsf {IV}}[11]}$
BBCDACEFDE80953A	C9891A2879725B3E	7C9FE6330237E440	A30BA550553F7431
${\displaystyle {\textsf {IV}}[12]}$	${\displaystyle {\textsf {IV}}[13]}$	${\displaystyle {\textsf {IV}}[14]}$	${\displaystyle {\textsf {IV}}[15]}$
BB08043FB34E3E30	A0DEC48D54618EAD	150317267464BC57	32D1501FDE63DC93

LSH-512-512 initialization vector

${\displaystyle {\textsf {IV}}[0]}$	${\displaystyle {\textsf {IV}}[1]}$	${\displaystyle {\textsf {IV}}[2]}$	${\displaystyle {\textsf {IV}}[3]}$
ADD50F3C7F07094E	E3F3CEE8F9418A4F	B527ECDE5B3D0AE9	2EF6DEC68076F501
${\displaystyle {\textsf {IV}}[4]}$	${\displaystyle {\textsf {IV}}[5]}$	${\displaystyle {\textsf {IV}}[6]}$	${\displaystyle {\textsf {IV}}[7]}$
8CB994CAE5ACA216	FBB9EAE4BBA48CC7	650A526174725FEA	1F9A61A73F8D8085
${\displaystyle {\textsf {IV}}[8]}$	${\displaystyle {\textsf {IV}}[9]}$	${\displaystyle {\textsf {IV}}[10]}$	${\displaystyle {\textsf {IV}}[11]}$
B6607378173B539B	1BC99853B0C0B9ED	DF727FC19B182D47	DBEF360CF893A457
${\displaystyle {\textsf {IV}}[12]}$	${\displaystyle {\textsf {IV}}[13]}$	${\displaystyle {\textsf {IV}}[14]}$	${\displaystyle {\textsf {IV}}[15]}$
4981F5E570147E80	D00C4490CA7D3E30	5D73940C0E4AE1EC	894085E2EDB2D819

In this stage, the ${\displaystyle t}$ 32-word array message blocks ${\displaystyle \{{\textsf {M}}^{(i)}\}_{i=0}^{t-1}}$, which are generated from a message ${\displaystyle m}$ in the initialization stage, are compressed by iteration of compression functions. The compression function ${\displaystyle {\textrm {CF}}:{\mathcal {W}}^{16}\times {\mathcal {W}}^{32}\rightarrow {\mathcal {W}}^{16}}$ has two inputs; the ${\displaystyle i}$-th 16-word chaining variable ${\displaystyle {\textsf {CV}}^{(i)}}$ and the ${\displaystyle i}$-th 32-word message block ${\displaystyle {\textsf {M}}^{(i)}}$. And it returns the ${\displaystyle (i+1)}$-th 16-word chaining variable ${\displaystyle {\textsf {CV}}^{(i+1)}}$. Here and subsequently, ${\displaystyle {\mathcal {W}}^{t}}$ denotes the set of all ${\displaystyle t}$-word arrays for ${\displaystyle t\geq 1}$.

The following four functions are used in a compression function:

• Message expansion function ${\displaystyle {\textrm {MsgExp}}:{\mathcal {W}}^{32}\rightarrow {\mathcal {W}}^{16(Ns+1)}}$
• Message addition function ${\displaystyle {\textrm {MsgAdd}}:{\mathcal {W}}^{16}\times {\mathcal {W}}^{16}\rightarrow {\mathcal {W}}^{16}}$
• Mix function ${\displaystyle {\textrm {Mix}}_{j}:{\mathcal {W}}^{16}\rightarrow {\mathcal {W}}^{16}}$
• Word-permutation function ${\displaystyle {\textrm {WordPerm}}:{\mathcal {W}}^{16}\rightarrow {\mathcal {W}}^{16}}$

The overall structure of the compression function is shown in the following figure.

In a compression function, the message expansion function ${\displaystyle {\textrm {MsgExp}}}$ generates ${\displaystyle (N_{s}+1)}$ 16-word array sub-messages ${\displaystyle \{{\textsf {M}}_{j}^{(i)}\}_{j=0}^{N_{s}}}$ from given ${\displaystyle {\textsf {M}}^{(i)}}$. Let ${\displaystyle {\textsf {T}}=(T[0],\ldots ,T[15])}$ be a temporary 16-word array set to the ${\displaystyle i}$-th chaining variable ${\displaystyle {\textsf {CV}}^{(i)}}$. The ${\displaystyle j}$-th step function ${\displaystyle {\textrm {Step}}_{j}}$ having two inputs ${\displaystyle {\textsf {T}}}$ and ${\displaystyle {\textsf {M}}_{j}^{(i)}}$ updates ${\displaystyle {\textsf {T}}}$, i.e., ${\displaystyle {\textsf {T}}\leftarrow {\textrm {Step}}_{j}\left({\textsf {T}},{\textsf {M}}_{j}^{(i)}\right)}$. All step functions are proceeded in order ${\displaystyle j=0,\ldots ,N_{s}-1}$. Then one more ${\displaystyle {\textrm {MsgAdd}}}$ operation by ${\displaystyle {\textsf {M}}_{N_{s}}^{(i)}}$ is proceeded, and the ${\displaystyle (i+1)}$-th chaining variable ${\displaystyle {\textsf {CV}}^{(i+1)}}$ is set to ${\displaystyle {\textsf {T}}}$. The process of a compression function in detail is as follows.

Here the ${\displaystyle j}$-th step function ${\displaystyle {\textrm {Step}}_{j}:{\mathcal {W}}^{16}\times {\mathcal {W}}^{16}\rightarrow {\mathcal {W}}^{16}}$ is as follows.

${\displaystyle {\textrm {Step}}_{j}:={\textrm {WordPerm}}\circ {\textrm {Mix}}_{j}\circ {\textrm {MsgAdd}}}$ ${\displaystyle (0\leq j\leq (N_{s}-1))}$

The following figure shows the ${\displaystyle j}$-th step function ${\displaystyle {\textrm {Step}}_{j}}$ of a compression function.

Let ${\displaystyle {\textsf {M}}^{(i)}=(M^{(i)}[0],\ldots ,M^{(i)}[31])}$ be the ${\displaystyle i}$-th 32-word array message block. The message expansion function ${\displaystyle {\textrm {MsgExp}}}$ generates ${\displaystyle (N_{s}+1)}$ 16-word array sub-messages ${\displaystyle \{{\textsf {M}}_{j}^{(i)}\}_{j=0}^{N_{s}}}$ from a message block ${\displaystyle {\textsf {M}}^{(i)}}$. The first two sub-messages ${\displaystyle {\textsf {M}}_{0}^{(i)}=(M_{0}^{(i)}[0],\ldots ,M_{0}^{(i)}[15])}$ and ${\displaystyle {\textsf {M}}_{1}^{(i)}=(M_{1}^{(i)}[0],\ldots ,M_{1}^{(i)}[15])}$ are defined as follows.

• ${\displaystyle {\textsf {M}}_{0}^{(i)}\leftarrow (M^{(i)}[0],M^{(i)}[1],\ldots ,M^{(i)}[15])}$
• ${\displaystyle {\textsf {M}}_{1}^{(i)}\leftarrow (M^{(i)}[16],M^{(i)}[17],\ldots ,M^{(i)}[31])}$

The next sub-messages ${\displaystyle \{{\textsf {M}}_{j}^{(i)}=(M_{j}^{(i)}[0],\ldots ,M_{j}^{(i)}[15])\}_{j=2}^{N_{s}}}$ are generated as follows.

• ${\displaystyle {\textsf {M}}_{j}^{(i)}[l]\leftarrow {\textsf {M}}_{j-1}^{(i)}[l]\boxplus {\textsf {M}}_{j-2}^{(i)}[\tau (l)]}$ ${\displaystyle (0\leq l\leq 15,\ 2\leq j\leq N_{s})}$

Here ${\displaystyle \tau }$ is the permutation over ${\displaystyle \mathbb {Z} _{16}}$ defined as follows.

The permutation ${\displaystyle \tau :\mathbb {Z} _{16}\rightarrow \mathbb {Z} _{16}}$

${\displaystyle l}$	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15
${\displaystyle \tau (l)}$	3	2	0	1	7	4	5	6	11	10	8	9	15	12	13	14

For two 16-word arrays ${\displaystyle {\textsf {X}}=(X[0],\ldots ,X[15])}$ and ${\displaystyle {\textsf {Y}}=(Y[0],\ldots ,Y[15])}$, the message addition function ${\displaystyle {\textrm {MsgAdd}}:{\mathcal {W}}^{16}\times {\mathcal {W}}^{16}\rightarrow {\mathcal {W}}^{16}}$ is defined as follows.

${\displaystyle {\textrm {MsgAdd}}({\textsf {X}},{\textsf {Y}}):=(X[0]\oplus Y[0],\ldots ,X[15]\oplus Y[15])}$

The ${\displaystyle j}$-th mix function ${\displaystyle {\textrm {Mix}}_{j}:{\mathcal {W}}^{16}\rightarrow {\mathcal {W}}^{16}}$ updates the 16-word array ${\displaystyle {\textsf {T}}=(T[0],\ldots ,T[15])}$ by mixing every two-word pair; ${\displaystyle T[l]}$ and ${\displaystyle T[l+8]}$ for ${\displaystyle (0\leq l<8)}$. For ${\displaystyle 0\leq j<N_{s}}$, the mix function ${\displaystyle {\textrm {Mix}}_{j}}$ proceeds as follows.

${\displaystyle (T[l],T[l+8])\leftarrow {\textrm {Mix}}_{j,l}(T[l],T[l+8])}$ ${\displaystyle (0\leq l<8)}$

Here ${\displaystyle {\textrm {Mix}}_{j,l}}$ is a two-word mix function. Let ${\displaystyle X}$ and ${\displaystyle Y}$ be words. The two-word mix function ${\displaystyle {\textrm {Mix}}_{j,l}:{\mathcal {W}}^{2}\rightarrow {\mathcal {W}}^{2}}$ is defined as follows.

The two-word mix function ${\displaystyle {\textrm {Mix}}_{j,l}}$ is shown in the following figure.

The bit rotation amounts ${\displaystyle \alpha _{j}}$, ${\displaystyle \beta _{j}}$, ${\displaystyle \gamma _{l}}$ used in ${\displaystyle {\textrm {Mix}}_{j,l}}$ are shown in the following table.

Bit rotation amounts ${\displaystyle \alpha _{j}}$, ${\displaystyle \beta _{j}}$, and ${\displaystyle \gamma _{l}}$

${\displaystyle w}$	${\displaystyle j}$	${\displaystyle \alpha _{j}}$	${\displaystyle \beta _{j}}$	${\displaystyle \gamma _{0}}$	${\displaystyle \gamma _{1}}$	${\displaystyle \gamma _{2}}$	${\displaystyle \gamma _{3}}$	${\displaystyle \gamma _{4}}$	${\displaystyle \gamma _{5}}$	${\displaystyle \gamma _{6}}$	${\displaystyle \gamma _{7}}$
32	even	29	1	0	8	16	24	24	16	8	0
	odd	5	17
64	even	23	59	0	16	32	48	8	24	40	56
	odd	7	3

The ${\displaystyle j}$-th 8-word array constant ${\displaystyle {\textsf {SC}}_{j}=(SC_{j}[0],\ldots ,SC_{j}[7])}$ used in ${\displaystyle {\textrm {Mix}}_{j,l}}$ for ${\displaystyle 0\leq l<8}$ is defined as follows. The initial 8-word array constant ${\displaystyle {\textsf {SC}}_{0}=(SC_{0}[0],\ldots ,SC_{0}[7])}$ is defined in the following table. For ${\displaystyle 1\leq j<N_{s}}$, the ${\displaystyle j}$-th constant ${\displaystyle {\textsf {SC}}_{j}=(SC_{j}[0],\ldots ,SC_{j}[7])}$ is generated by ${\displaystyle SC_{j}[l]\leftarrow SC_{j-1}[l]\boxplus SC_{j-1}[l]^{\lll 8}}$ for ${\displaystyle 0\leq l<8}$.

Initial 8-word array constant ${\displaystyle {\textsf {SC}}_{0}}$

	${\displaystyle w=32}$	${\displaystyle w=64}$
${\displaystyle SC_{0}[0]}$	917caf90	97884283c938982a
${\displaystyle SC_{0}[1]}$	6c1b10a2	ba1fca93533e2355
${\displaystyle SC_{0}[2]}$	6f352943	c519a2e87aeb1c03
${\displaystyle SC_{0}[3]}$	cf778243	9a0fc95462af17b1
${\displaystyle SC_{0}[4]}$	2ceb7472	fc3dda8ab019a82b
${\displaystyle SC_{0}[5]}$	29e96ff2	02825d079a895407
${\displaystyle SC_{0}[6]}$	8a9ba428	79f2d0a7ee06a6f7
${\displaystyle SC_{0}[7]}$	2eeb2642	d76d15eed9fdf5fe

Let ${\displaystyle {\textsf {X}}=(X[0],\ldots ,X[15])}$ be a 16-word array. The word-permutation function ${\displaystyle {\textrm {WordPerm}}:{\mathcal {W}}^{16}\rightarrow {\mathcal {W}}^{16}}$ is defined as follows.

${\displaystyle {\textrm {WordPerm}}({\textsf {X}})=(X[\sigma (0)],\ldots ,X[\sigma (15)])}$

Here ${\displaystyle \sigma }$ is the permutation over ${\displaystyle \mathbb {Z} _{16}}$ defined by the following table.

The permutation ${\displaystyle \sigma :\mathbb {Z} _{16}\rightarrow \mathbb {Z} _{16}}$

${\displaystyle l}$	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15
${\displaystyle \sigma (l)}$	6	4	5	7	12	15	14	13	2	0	1	3	8	11	10	9

The finalization function ${\displaystyle {\textrm {FIN}}_{n}:{\mathcal {W}}^{16}\rightarrow \{0,1\}^{n}}$ returns ${\displaystyle n}$-bit hash value ${\displaystyle h}$ from the final chaining variable ${\displaystyle {\textsf {CV}}^{(t)}=(CV^{(t)}[0],\ldots ,CV^{(t)}[15])}$. When ${\displaystyle {\textsf {H}}=(H[0],\ldots ,H[7])}$ is an 8-word variable and ${\displaystyle {\textsf {h}}_{\textsf {b}}=(h_{b}[0],\ldots ,h_{b}[w-1])}$ is a ${\displaystyle w}$-byte variable, the finalization function ${\displaystyle {\textrm {FIN}}_{n}}$ performs the following procedure.

• ${\displaystyle H[l]\leftarrow CV^{(t)}[l]\oplus CV^{(t)}[l+8]}$ ${\displaystyle (0\leq l\leq 7)}$
• ${\displaystyle h_{b}[s]\leftarrow H[\lfloor 8s/w\rfloor ]_{[7:0]}^{\ggg (8s\mod w)}}$ ${\displaystyle (0\leq s\leq (w-1))}$
• ${\displaystyle h\leftarrow (h_{b}[0]\|\ldots \|h_{b}[w-1])_{[0:n-1]}}$

Here, ${\displaystyle X_{[i:j]}}$ denotes ${\displaystyle x_{i}\|x_{i-1}\|\ldots \|x_{j}}$, the sub-bit string of a word ${\displaystyle X}$ for ${\displaystyle i\geq j}$. And ${\displaystyle x_{[i:j]}}$ denotes ${\displaystyle x_{i}\|x_{i+1}\|\ldots \|x_{j}}$, the sub-bit string of a ${\displaystyle l}$-bit string ${\displaystyle x=x_{0}\|x_{1}\|\ldots \|x_{l-1}}$ for ${\displaystyle i\leq j}$.

LSH is secure against known attacks on hash functions up to now. LSH is collision-resistant for ${\displaystyle q<2^{n/2}}$ and preimage-resistant and second-preimage-resistant for ${\displaystyle q<2^{n}}$ in the ideal cipher model, where ${\displaystyle q}$ is a number of queries for LSH structure.^[1] LSH-256 is secure against all the existing hash function attacks when the number of steps is 13 or more, while LSH-512 is secure if the number of steps is 14 or more. Note that the steps which work as security margin are 50% of the compression function.^[1]

LSH outperforms SHA-2/3 on various software platforms. The following table shows the speed performance of 1MB message hashing of LSH on several platforms.

1MB message hashing speed of LSH (cycles/byte)^[1]

Platform	P1[a]	P2[b]	P3[c]	P4[d]	P5[e]	P6[f]	P7[g]	P8[h]
LSH-256-${\displaystyle n}$	3.60	3.86	5.26	3.89	11.17	15.03	15.28	14.84
LSH-512-${\displaystyle n}$	2.39	5.04	7.76	5.52	8.94	18.76	19.00	18.10

The following table is the comparison at the platform based on Haswell, LSH is measured on Intel Core i7-4770k @ 3.5 GHz quad core platform, and others are measured on Intel Core i5-4570S @ 2.9 GHz quad core platform.

The following table is measured on Samsung Exynos 5250 ARM Cortex-A15 @ 1.7 GHz dual core platform.

Test vectors for LSH for each digest length are as follows. All values are expressed in hexadecimal form.

LSH-256-224("abc") = F7 C5 3B A4 03 4E 70 8E 74 FB A4 2E 55 99 7C A5 12 6B B7 62 36 88 F8 53 42 F7 37 32

LSH-256-256("abc") = 5F BF 36 5D AE A5 44 6A 70 53 C5 2B 57 40 4D 77 A0 7A 5F 48 A1 F7 C1 96 3A 08 98 BA 1B 71 47 41

LSH-512-224("abc") = D1 68 32 34 51 3E C5 69 83 94 57 1E AD 12 8A 8C D5 37 3E 97 66 1B A2 0D CF 89 E4 89

LSH-512-256("abc") = CD 89 23 10 53 26 02 33 2B 61 3F 1E C1 1A 69 62 FC A6 1E A0 9E CF FC D4 BC F7 58 58 D8 02 ED EC

LSH-512-384("abc") = 5F 34 4E FA A0 E4 3C CD 2E 5E 19 4D 60 39 79 4B 4F B4 31 F1 0F B4 B6 5F D4 5E 9D A4 EC DE 0F 27 B6 6E 8D BD FA 47 25 2E 0D 0B 74 1B FD 91 F9 FE

LSH-512-512("abc") = A3 D9 3C FE 60 DC 1A AC DD 3B D4 BE F0 A6 98 53 81 A3 96 C7 D4 9D 9F D1 77 79 56 97 C3 53 52 08 B5 C5 72 24 BE F2 10 84 D4 20 83 E9 5A 4B D8 EB 33 E8 69 81 2B 65 03 1C 42 88 19 A1 E7 CE 59 6D

LSH is free for any use public or private, commercial or non-commercial. The source code for distribution of LSH implemented in C, Java, and Python can be downloaded from KISA's cryptography use activation webpage.^[2]

LSH is one of the cryptographic algorithms approved by the Korean Cryptographic Module Validation Program (KCMVP).^[3]

LSH is included in the following standard.

• KS X 3262, Hash function LSH (in Korean)^[4]