1 files changed, 192 insertions, 0 deletions
diff --git a/lib/sha256.go b/lib/sha256.go
new file mode 100644
index 0000000..da6dd7c
--- /dev/null
+++ b/lib/sha256.go
@@ -0,0 +1,192 @@
+// Copyright © 2022 siddharth <s@ricketyspace.net>
+// SPDX-License-Identifier: ISC
+
+package lib
+
+// SHA-256 implementation.
+// Reference https://csrc.nist.gov/publications/detail/fips/180/4/final
+
+type Sha256 struct {
+	hvs    []uint32
+	Msg    []byte
+	MsgLen int
+}
+
+// SHA-256 Constants
+var sha256K []uint32 = []uint32{
+	0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5,
+	0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3, 0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174,
+	0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc, 0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
+	0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7, 0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967,
+	0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13, 0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
+	0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3, 0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
+	0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
+	0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208, 0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2,
+}
+
+// SHA-256 initial hash values.
+var sha256HashValues []uint32 = []uint32{
+	0x6a09e667,
+	0xbb67ae85,
+	0x3c6ef372,
+	0xa54ff53a,
+	0x510e527f,
+	0x9b05688c,
+	0x1f83d9ab,
+	0x5be0cd19,
+}
+
+// Ch(x,y,z) function.
+func sha256FCh(x, y, z uint32) uint32 {
+	return (x & y) ^ (^x & z)
+}
+
+// Maj(x,y,z) function.
+func sha256FMaj(x, y, z uint32) uint32 {
+	return (x & y) ^ (x & z) ^ (y & z)
+}
+
+// Σ0(x) function.
+func sha256FΣ0(x uint32) uint32 {
+	return shaRotr(x, 2) ^ shaRotr(x, 13) ^ shaRotr(x, 22)
+}
+
+// Σ1(x) function.
+func sha256FΣ1(x uint32) uint32 {
+	return shaRotr(x, 6) ^ shaRotr(x, 11) ^ shaRotr(x, 25)
+}
+
+// σ0(x) function.
+func sha256Fσ0(x uint32) uint32 {
+	return shaRotr(x, 7) ^ shaRotr(x, 18) ^ shaShr(x, 3)
+}
+
+// σ1(x) function.
+func sha256Fσ1(x uint32) uint32 {
+	return shaRotr(x, 17) ^ shaRotr(x, 19) ^ shaShr(x, 10)
+}
+
+// Returns the message schedule W_t for a message block `mb`
+// The message schedule has 64 32-bit words.
+func sha256MessageSchedule(mb []uint32) []uint32 {
+	// Message schedule.
+	w := make([]uint32, 0)
+
+	// Generate message schedule.
+	for t := 0; t < 64; t++ {
+		if t <= 15 {
+			w = append(w, mb[t])
+		} else {
+			w = append(w, shaAdd(
+				sha256Fσ1(w[t-2]),
+				w[t-7],
+				sha256Fσ0(w[t-15]),
+				w[t-16],
+			))
+		}
+	}
+	return w
+}
+
+func (s *Sha256) Init(hvs []uint32) {
+	// Set initial hash values.
+	h := make([]uint32, 8)
+	if len(hvs) == 8 {
+		copy(h, hvs)
+		s.hvs = h
+	} else {
+		copy(h, sha256HashValues)
+		s.hvs = h
+	}
+}
+
+func (s *Sha256) Message(m []byte) {
+	s.Msg = m
+	s.MsgLen = len(m)
+}
+
+// SHA-256 - Pad message such that its length is a multiple of 512.
+func (s *Sha256) Pad() []byte {
+	// Initialize padded message.
+	pm := make([]byte, len(s.Msg))
+	copy(pm, s.Msg)
+
+	// Add padding.
+	pm = append(pm, MDPadding(s.MsgLen)...)
+
+	return pm
+}
+
+func (s *Sha256) Hash() []byte {
+	// Pad message.
+	pm := s.Pad()
+
+	// Break int message blocks.
+	mbs := shaMessageBlocks(pm)
+
+	// Initialize hash values.
+	hvs := make([]uint32, 8)
+	copy(hvs, s.hvs) // Initial hash values.
+
+	// Process each message block.
+	for _, mb := range mbs {
+		// Get message schedule.
+		w := sha256MessageSchedule(mb)
+
+		// Initialize working variables.
+		a := hvs[0]
+		b := hvs[1]
+		c := hvs[2]
+		d := hvs[3]
+		e := hvs[4]
+		f := hvs[5]
+		g := hvs[6]
+		h := hvs[7]
+
+		for t := 0; t <= 63; t++ {
+			t1 := shaAdd(
+				h,
+				sha256FΣ1(e),
+				sha256FCh(e, f, g),
+				sha256K[t],
+				w[t],
+			)
+			t2 := shaAdd(sha256FΣ0(a), sha256FMaj(a, b, c))
+			h = g
+			g = f
+			f = e
+			e = shaAdd(d, t1)
+			d = c
+			c = b
+			b = a
+			a = shaAdd(t1, t2)
+		}
+
+		// Compute intermediate hash values.
+		hvs[0] = shaAdd(a, hvs[0])
+		hvs[1] = shaAdd(b, hvs[1])
+		hvs[2] = shaAdd(c, hvs[2])
+		hvs[3] = shaAdd(d, hvs[3])
+		hvs[4] = shaAdd(e, hvs[4])
+		hvs[5] = shaAdd(f, hvs[5])
+		hvs[6] = shaAdd(g, hvs[6])
+		hvs[7] = shaAdd(h, hvs[7])
+	}
+
+	// Slurp sha256 digest from hash values.
+	d := make([]byte, 0) // sha256 digest
+	for i := 0; i < 8; 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(hvs[i] & 0xFF)
+
+			// Get rid of last 8 bits.
+			hvs[i] = hvs[i] >> 8
+		}
+		d = append(d, hb...)
+	}
+
+	return d
+}