; file: sha256.s
; SHA-256 cryptographic hash
;
; Implementation is based on <Wikipedia's pseudocode at https://en.wikipedia.org/wiki/SHA-2#Pseudocode>
;
; About: CPU compatibility
; /!\ Only work on *486+* due to bswap for now.
[BITS 32]

section .rodata
; Constant: K
; SHA-256 round constants 
K:
	dd 0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5,
	dd 0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3, 0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174,
	dd 0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc, 0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
	dd 0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7, 0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967,
	dd 0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13, 0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
	dd 0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3, 0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
	dd 0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
	dd 0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208, 0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2

section .text

	; Function: sha256_compute_block
sha256_compute_block:
	push ebp
	mov ebp, esp

	leave
	ret

	; Function: sha256_internal
	; 
	; in:
	;      - state
	;      - Input buffer
	;      - Input buffer size
	;
	; out:
	;     none
	;
sha256_internal:
	push ebp
	push edi
	mov ebp, esp
	sub esp, 64+8

	mov eax, dword [ebp+16]
	xor edx, edx

	; set padlen to (len << 3)
	shld edx, eax, 3 ;  64-bit left shit
	sal eax, 3
	mov dword [ebp-(64+8)], eax
	mov dword [ebp-(64+4)], edx

.for_block:
	cmp dword [ebp+16], 64
	jb .done
	push dword [ebp+12] ; push in
	push dword [ebp+8]  ; push state
	call sha256_compute_block
	add esp, 8
	sub dword [ebp+16], 64 ; len -= 64
	add dword [ebp+12], 64 ; in += 64
	jmp .for_block
.done:

	; ensure padding buffer is full of zero
	lea edi, [ebp-64]
	mov ecx, 16
	xor eax, eax
	rep stosd

	

	pop edi
	leave
	ret

	; Function: sha256
	; 
	; in:
	;      - Output buffer
	;      - Input buffer
	;      - Input buffer size
	;
	; out:
	;     none
	;
global sha256
sha256:
	push ebp
	mov ebp, esp
	sub esp, 8*4 ; uint32_t state[8]

	; setup initial state
	mov dword [ebp-8*4], 0x6a09e667
	mov dword [ebp-7*4], 0xbb67ae85
	mov dword [ebp-6*4], 0x3c6ef372
	mov dword [ebp-5*4], 0xa54ff53a
	mov dword [ebp-4*4], 0x510e527f
	mov dword [ebp-3*4], 0x9b05688c
	mov dword [ebp-2*4], 0x1f83d9ab
	mov dword [ebp-1*4], 0x5be0cd19

	; 

	; copy state to uint8_t *out
	mov edx, dword [ebp+8]
	mov eax, dword [ebp-8*4]
	bswap eax
	mov dword [edx], eax      ; out[0] = bswap(state[0])
	mov eax, dword [ebp-7*4] 
	bswap eax
	mov dword [edx+4], eax    ; out[1] = bswap(state[1])
	mov eax, dword [ebp-6*4]
	bswap eax
	mov dword [edx+8], eax    ; out[2] = bswap(state[2])
	mov eax, dword [ebp-5*4]
	bswap eax
	mov dword [edx+12], eax   ; out[3] = bswap(state[3])
	mov eax, dword [ebp-4*4]
	bswap eax
	mov dword [edx+16], eax   ; out[4] = bswap(state[4])
	mov eax, dword [ebp-3*4]
	bswap eax
	mov dword [edx+20], eax   ; out[5] = bswap(state[5])
	mov eax, dword [ebp-2*4]
	bswap eax
	mov dword [edx+24], eax   ; out[6] = bswap(state[6])
	mov eax, dword [ebp-1*4]
	bswap eax
	mov dword [edx+28], eax   ; out[7] = bswap(state[7])
	leave
	ret