1 files changed, 209 insertions, 0 deletions
diff --git a/lib/sha1.go b/lib/sha1.go
new file mode 100644
index 0000000..3596160
--- /dev/null
+++ b/lib/sha1.go
@@ -0,0 +1,209 @@
+// 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
+}