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-rw-r--r--lib/sha1.go209
1 files changed, 209 insertions, 0 deletions
diff --git a/lib/sha1.go b/lib/sha1.go
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+// Copyright © 2021 rsiddharth <s@ricketyspace.net>
+// SPDX-License-Identifier: ISC
+
+package lib
+
+// SHA-1 implementation.
+// Reference https://csrc.nist.gov/publications/detail/fips/180/4/final
+
+// Initial hash value.
+var sha1IHashValue []uint32 = []uint32{
+ 0x67452301,
+ 0xefcdab89,
+ 0x98badcfe,
+ 0x10325476,
+ 0xc3d2e1f0,
+}
+
+// (a + b + ...) mod 2^32
+func sha1Add(n ...uint32) uint32 {
+ sum := uint64(0)
+ for _, v := range n {
+ sum += uint64(v)
+ }
+ return uint32(sum & 0xFFFFFFFF)
+}
+
+// Circular Right Shift
+func sha1Rotr(x uint32, n uint) uint32 {
+ return (x >> n) | (x << (32 - n))
+}
+
+// Circular Left Shift
+func sha1Rotl(x uint32, n uint) uint32 {
+ return (x << n) | (x >> (32 - n))
+}
+
+// SHA-1 - Function f_t(x, y, z)
+func sha1FT(t int, x, y, z uint32) uint32 {
+ switch {
+ case t <= 19:
+ return (x & y) ^ (^x & z)
+ case t >= 20 && t <= 39:
+ return x ^ y ^ z
+ case t >= 40 && t <= 59:
+ return (x & y) ^ (x & z) ^ (y & z)
+ case t >= 60 && t <= 79:
+ return x ^ y ^ z
+ default:
+ return uint32(0)
+ }
+}
+
+// SHA-1 - Constant K_t
+func sha1KT(t int) uint32 {
+ switch {
+ case t <= 19:
+ return uint32(0x5a827999)
+ case t >= 20 && t <= 39:
+ return uint32(0x6ed9eba1)
+ case t >= 40 && t <= 59:
+ return uint32(0x8f1bbcdc)
+ case t >= 60 && t <= 79:
+ return uint32(0xca62c1d6)
+ default:
+ return uint32(0)
+ }
+}
+
+// SHA-1 - Pad message such that its length is a multiple of 512.
+func sha1Pad(m []byte) []byte {
+ l := len(m) * 8 // msg size in bits
+
+ // Reckon value of `k`
+ k := 0
+ for ((l + 1 + k) % 512) != 448 {
+ k += 1
+ }
+
+ // Initialize padded message
+ pm := make([]byte, len(m))
+ copy(pm, m)
+
+ // Add bit `1` as byte block.
+ pm = append(pm, 0x80)
+ f := 7 // unclaimed bits in last byte of `pm`
+
+ // Add `k` bit `0`s
+ for i := 0; i < k; i++ {
+ if f == 0 {
+ pm = append(pm, 0x0)
+ f = 8
+ }
+ f = f - 1
+ }
+
+ // Add `l` in a 64 bit block in `pm`
+ l64 := uint64(l)
+ b64 := make([]byte, 8) // last 64-bits
+ for i := 7; i >= 0; i-- {
+ // Get 8 last bits.
+ b64[i] = byte(l64 & 0xFF)
+
+ // Get rid of the last 8 bits.
+ l64 = l64 >> 8
+ }
+ pm = append(pm, b64...)
+
+ return pm
+}
+
+// Converts padded messages bytes `pm` into 512-bit message blocks.
+// Each 512-bit block is an array of 16 32-bit words.
+func sha1MessageBlocks(pm []byte) [][]uint32 {
+ // Break into 512-bit blocks
+ bs := BreakIntoBlocks(pm, 64)
+
+ mbs := make([][]uint32, 0) // Message blocks.
+ for i := 0; i < len(bs); i++ {
+ ws := make([]uint32, 0) // 32-bit words.
+
+ // Break 512-bit (64 bytes) into 32-bit words.
+ for j := 0; j < 64; j = j + 4 {
+ // Pack 4 bytes into a 32-bit word.
+ w := (uint32(bs[i][j])<<24 |
+ uint32(bs[i][j+1])<<16 |
+ uint32(bs[i][j+2])<<8 |
+ uint32(bs[i][j+3]))
+ ws = append(ws, w)
+ }
+ mbs = append(mbs, ws)
+ }
+ return mbs
+}
+
+// Returns the message schedule W_t for message black `mb`
+// The message schedule has 80 32-bit words.
+func sha1MessageSchedule(mb []uint32) []uint32 {
+ // Message schedule.
+ w := make([]uint32, 0)
+
+ // Generate message schedule.
+ for t := 0; t <= 79; t++ {
+ if t <= 15 {
+ w = append(w, mb[t])
+ } else {
+ w = append(w, sha1Rotl(w[t-3]^w[t-8]^w[t-14]^w[t-16], 1))
+ }
+ }
+ return w
+}
+
+func Sha1(m []byte) []byte {
+ // Pad message.
+ pm := sha1Pad(m)
+
+ // Break into message blocks.
+ mbs := sha1MessageBlocks(pm)
+
+ // Initialize hash values.
+ h := make([]uint32, 5)
+ copy(h, sha1IHashValue) // Initial hash values.
+
+ // Process each message block.
+ for _, mb := range mbs {
+ // Get message schedule.
+ w := sha1MessageSchedule(mb)
+
+ // Initialize working variables.
+ a := h[0]
+ b := h[1]
+ c := h[2]
+ d := h[3]
+ e := h[4]
+
+ for t := 0; t <= 79; t++ {
+ tmp := sha1Add(sha1Rotl(a, 5), sha1FT(t, b, c, d),
+ e, sha1KT(t), w[t])
+ e = d
+ d = c
+ c = sha1Rotl(b, 30)
+ b = a
+ a = tmp
+ }
+
+ // Compute intermediate hash values.
+ h[0] = sha1Add(a, h[0])
+ h[1] = sha1Add(b, h[1])
+ h[2] = sha1Add(c, h[2])
+ h[3] = sha1Add(d, h[3])
+ h[4] = sha1Add(e, h[4])
+ }
+
+ // Slurp sha1 digest from hash values.
+ d := make([]byte, 0) // sha1 digest
+ for i := 0; i < 5; i++ {
+ // Break 32-bit hash value into 4 bytes.
+ hb := make([]byte, 4)
+ for j := 3; j >= 0; j-- {
+ // Get last 8 bits.
+ hb[j] = byte(h[i] & 0xFF)
+
+ // Get rid of last 8 bits.
+ h[i] = h[i] >> 8
+ }
+ d = append(d, hb...)
+ }
+
+ return d
+}