packer.sacara

proc data_section
S:
	// Hardcode the initial state of the S array
	byte 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F
	byte 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1A, 0x1B, 0x1C, 0x1D, 0x1E, 0x1F
	byte 0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28, 0x29, 0x2A, 0x2B, 0x2C, 0x2D, 0x2E, 0x2F
	byte 0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3A, 0x3B, 0x3C, 0x3D, 0x3E, 0x3F
	byte 0x40, 0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4A, 0x4B, 0x4C, 0x4D, 0x4E, 0x4F
	byte 0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5A, 0x5B, 0x5C, 0x5D, 0x5E, 0x5F
	byte 0x60, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6A, 0x6B, 0x6C, 0x6D, 0x6E, 0x6F
	byte 0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7A, 0x7B, 0x7C, 0x7D, 0x7E, 0x7F
	byte 0x80, 0x81, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87, 0x88, 0x89, 0x8A, 0x8B, 0x8C, 0x8D, 0x8E, 0x8F
	byte 0x90, 0x91, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97, 0x98, 0x99, 0x9A, 0x9B, 0x9C, 0x9D, 0x9E, 0x9F
	byte 0xA0, 0xA1, 0xA2, 0xA3, 0xA4, 0xA5, 0xA6, 0xA7, 0xA8, 0xA9, 0xAA, 0xAB, 0xAC, 0xAD, 0xAE, 0xAF
	byte 0xB0, 0xB1, 0xB2, 0xB3, 0xB4, 0xB5, 0xB6, 0xB7, 0xB8, 0xB9, 0xBA, 0xBB, 0xBC, 0xBD, 0xBE, 0xBF
	byte 0xC0, 0xC1, 0xC2, 0xC3, 0xC4, 0xC5, 0xC6, 0xC7, 0xC8, 0xC9, 0xCA, 0xCB, 0xCC, 0xCD, 0xCE, 0xCF
	byte 0xD0, 0xD1, 0xD2, 0xD3, 0xD4, 0xD5, 0xD6, 0xD7, 0xD8, 0xD9, 0xDA, 0xDB, 0xDC, 0xDD, 0xDE, 0xDF
	byte 0xE0, 0xE1, 0xE2, 0xE3, 0xE4, 0xE5, 0xE6, 0xE7, 0xE8, 0xE9, 0xEA, 0xEB, 0xEC, 0xED, 0xEE, 0xEF
	byte 0xF0, 0xF1, 0xF2, 0xF3, 0xF4, 0xF5, 0xF6, 0xF7, 0xF8, 0xF9, 0xFA, 0xFB, 0xFC, 0xFD, 0xFE, 0xFF
	
	// add a halt to make it syntax valid and avoid assembler warning.
	// It is safe to add halt since it will never be executed
	halt
endp

proc decode_password(pwd, pwd_len)	
	.mov index, 0
	
decode_pwd_loop:
	// read the byte to decode
	.mov pwd_offset, (pwd + index)
	.nread.b pwd_offset	
	pop xored_char
	
	// decode the byte with hardcoded key
	.xor xored_char, 0xA1
	
	// write back the result
	pop xored_char
	.nwrite.b pwd_offset, xored_char
	
	// check if completed
	.inc index
	.cmp index, pwd_len	
	push decode_pwd_loop
	jumpifl 
	
	ret
endp

proc swap(i, j)
	.read.b (S + i)
	pop S_i

	.read.b (S + j)
	pop S_j
	
	// swap the values
	.write.b (S + i), S_j
	.write.b (S + j), S_i	
	
	ret
endp

proc ksa(password, password_length)
	.mov i, 0
	.mov j, 0

ksa_loop:
	// read the i-th byte from S array
	.read.b (S + i)
	pop S_i
	
	// read the i-th byte from password
	.nread.b (password + (i % password_length))
	pop pwd_i
	
	// compute loop expression
	.mov j, ((j + S_i + pwd_i) % 256)	
	.swap(i, j)
	
	// check if I have to iterate
	.inc i	
	.cmp i, 256
	push ksa_loop
	jumpifl	
	ret
endp

proc prga(buffer, buffer_length)
	.mov i, 0
	.mov j, 0
	.mov n, 0
	
prga_loop:
	// update index i
	.mov i, ((i + 1) % 256)	
	
	// update index j
	.read.b (S + i)	
	pop S_i
	.mov j, ((j + S_i) % 256)
	
	// swap
	.swap(i, j)
	
	// read indexes
	.read.b (S + i)	
	pop S_i
	
	.read.b (S + j)	
	pop S_j
	
	// compute random
	.read.b (S + ((S_i + S_j) % 256))
	pop rnd
	
	// read n-th buffer value
	.nread.b (buffer + n)
	pop buffer_n	
	
	// XOR with buffer and write back the result	
	.xor buffer_n, rnd
	pop encrypted_char
	.nwrite.b (buffer + n), encrypted_char	

	// check if I have to iterate
	.inc n
	.cmp n, buffer_length
	push prga_loop
	jumpifl
	
	ret
endp

proc main(buffer, buffer_length, password, password_length)
	.mov result, 0
		
	// invoke the routine to decode the password
	.decode_password(password, password_length)
	
	// do KSA phase
	.ksa(password, password_length)	
	
	// do PRGA phase and write back the result
	.prga(buffer, buffer_length)
	
	// finally invoke the native method
	.ncall(buffer)
	
	halt
endp