// Copyright © 2022 siddharth ravikumar <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
}
func (s *Sha256) Mac(secret, msg []byte) []byte {
s.Message(append(secret, msg...))
return s.Hash()
}
func (s *Sha256) MacVerify(secret, msg, mac []byte) bool {
s.Message(append(secret, msg...))
if BytesEqual(s.Hash(), mac) {
return true
}
return false
}
// HMAC-SHA256.
func HmacSha256(key, msg []byte) []byte {
// Initialize SHA-256 object.
sha := Sha256{}
sha.Init([]uint32{})
// Modify key based on it's size.
if len(key) > 64 { // > blocksize (64 bytes)
sha.Message(key)
key = sha.Hash()
}
if len(key) < 64 { // < blocksize (64 bytes)
// Pad with zeroes up to 64 bytes.
key = append(key, make([]byte, 64-len(key))...)
}
// Outer padded key.
opk := FixedXORBytes(key, FillBytes(0x5c, 64))
// Inner padded key.
ipk := FixedXORBytes(key, FillBytes(0x36, 64))
return sha.Mac(opk, sha.Mac(ipk, msg))
}
