From 65f1016427f349073387b89a16e0e0b67a0692e3 Mon Sep 17 00:00:00 2001
From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: Sat, 13 Oct 2018 06:16:22 +0200
Subject: Simplify crypto

---
 Makefile  |  4 ++--
 hasplib.c | 51 ++++++++++++++++++++++++++-------------------------
 2 files changed, 28 insertions(+), 27 deletions(-)

diff --git a/Makefile b/Makefile
index 66561f1..392a748 100644
--- a/Makefile
+++ b/Makefile
@@ -1,4 +1,4 @@
-CFLAGS ?= -O3 -march=native -fomit-frame-pointer -pipe
+CFLAGS ?= -O3 -march=native -pipe
 
 CFLAGS += -std=c99 $(shell pkg-config --cflags libusb-1.0)
 LDLIBS = $(shell pkg-config --libs libusb-1.0)
@@ -11,6 +11,6 @@ hasplib-simple.c: hasplib.c hasplib.h
 test: hasplib.c hasplib-simple.c test.c
 
 clean:
-	rm -v test
+	@rm -fv test
 
 .PHONY: all clean
diff --git a/hasplib.c b/hasplib.c
index 70170da..455d194 100644
--- a/hasplib.c
+++ b/hasplib.c
@@ -23,20 +23,18 @@
 #include <string.h>
 #include <libusb.h>
 
-#pragma pack(1)
 struct hasp_response {
 	uint8_t status;
 	uint8_t status_checksum;
 	uint8_t data[16];
 };
-#pragma pack()
 
 struct _hasp_dongle {
 	libusb_device_handle *handle;
 	bool initialized;
 	
-	uint16_t cipher_key1;
-	uint16_t cipher_key2;
+	uint16_t lfsr;
+	uint16_t polynomial_bottom;
 	
 	uint16_t password1;
 	uint16_t password2;
@@ -53,34 +51,37 @@ enum HASP_FUNCTION_LIST {
 };
 
 enum HASP_STATUS {
-	HASP_STATUS_OK                     = 0,  
-	HASP_STATUS_ERROR                  = 1,  
-	HASP_STATUS_INVALID_MEMORY_ADDRESS = 4,  
+	HASP_STATUS_OK                     = 0x00,
+	HASP_STATUS_ERROR                  = 0x01,
+	HASP_STATUS_INVALID_MEMORY_ADDRESS = 0x04,
 	HASP_STATUS_LAST                   = 0x1F,
 	HASP_USB_ERROR                     = 0x6D
 };
 
 static void cipher(hasp_dongle *dongle, uint8_t *buffer, size_t len)
 {
-	uint16_t key1 = dongle->cipher_key1, key2 = dongle->cipher_key2;
-	uint8_t xor_byte, multiplier;
+	const uint16_t polynomial = (dongle->polynomial_bottom >> 1) | 0x8000;
+	uint16_t lfsr = dongle->lfsr;
+	uint8_t stream_byte, output_bit;
 
 	while (len--) {
-		xor_byte = 0;
+		stream_byte = 0;
 		for (int i = 0; i < 4; ++i) {
-			multiplier = xor_byte << 1;
-			if (key1 & 1) {
-				multiplier |= 1;
-				key1 = ((key1 ^ key2) >> 1) | 0x8000;
-			} else
-				key1 >>= 1;
-			xor_byte = multiplier << 1;
-			if (key1 & 0x80)
-				xor_byte |= 1;
+			/* Output a bit from position 0 into stream_byte. */
+			output_bit = lfsr & 1;
+			stream_byte = (stream_byte << 1) | output_bit;
+			lfsr >>= 1;
+
+			/* Flip the tap bits if we output a 1. */
+			lfsr ^= (-output_bit) & polynomial;
+
+			/* Output a bit from position 7 into stream_byte. */
+			output_bit = (lfsr >> 7) & 1;
+			stream_byte = (stream_byte << 1) | output_bit;
 		}
-		*(buffer++) ^= xor_byte;
+		*(buffer++) ^= stream_byte;
 	}
-	dongle->cipher_key1 = key1;
+	dongle->lfsr = lfsr;
 }
 
 static void usb_error(int error)
@@ -108,7 +109,7 @@ static void make_request(hasp_dongle *dongle, uint8_t function, uint16_t param1,
 	cipher(dongle, (uint8_t *)response, expected_data_len + 2);
 	
 	if (response->status == HASP_STATUS_OK)
-		   dongle->cipher_key2 = (dongle->cipher_key2 & 0xFF) | (response->status_checksum << 8);
+		   dongle->polynomial_bottom = (dongle->polynomial_bottom & 0xFF) | (response->status_checksum << 8);
 	else if (retry && dongle->password1 && dongle->password2) {
 		if (hasp_init(dongle) && hasp_login(dongle, dongle->password1, dongle->password2, NULL))
 			make_request(dongle, function, param1, param2, expected_data_len, cipher_params, false, response);
@@ -203,11 +204,11 @@ void hasp_free_dongle(hasp_dongle *dongle)
 
 bool hasp_init(hasp_dongle *dongle)
 {
-	dongle->cipher_key1 = 0xFABE;
-	dongle->cipher_key2 = 0xA0CB;
+	dongle->lfsr = 0xFABE;
+	dongle->polynomial_bottom = 0xA0CB;
 	
 	struct hasp_response response;
-	make_request(dongle, HASP_FUNCTION_SET_KEYS, dongle->cipher_key1, 0 /* unused */, 5, false, false, &response);
+	make_request(dongle, HASP_FUNCTION_SET_KEYS, dongle->lfsr, 0 /* unused */, 5, false, false, &response);
 	
 	if (response.status == HASP_STATUS_OK && response.data[0] == 0x2 && response.data[1] == 0xEA /* 0x0A? */ && response.data[2] == 0x00) {
 		dongle->initialized = true;
-- 
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