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// Copyright © 2021 rsiddharth <s@ricketyspace.net>
// SPDX-License-Identifier: ISC
package lib
// Converts padded messages bytes `pm` into 512-bit message blocks.
// Each 512-bit block is an array of 16 32-bit words.
// It's assumed bit length of `pm` is a multiple of 512.
func shaMessageBlocks(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 Merkle–Damgård padding in bytes for length of mesage `l`
// bytes.
func MDPadding(l int) []byte {
l = l * 8 // msg size in bits
// Reckon value of `k`
k := 0
for ((l + 1 + k) % 512) != 448 {
k += 1
}
// Initialize padding bytes
pbs := make([]byte, 0)
// Add bit `1` as byte block.
pbs = append(pbs, 0x80)
f := 7 // unclaimed bits in last byte of `pbs`
// Add `k` bit `0`s
for i := 0; i < k; i++ {
if f == 0 {
pbs = append(pbs, 0x0)
f = 8
}
f = f - 1
}
// Add `l` in a 64 bit block in `pbs`
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
}
pbs = append(pbs, b64...)
return pbs
}
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