From 594a56d164289747a58eae6758efea0dba92de61 Mon Sep 17 00:00:00 2001
From: Simon Waldherr <git@simon.waldherr.eu>
Date: Wed, 23 Oct 2024 19:55:12 +0200
Subject: [PATCH] add sha1 hashing

---
 hashing/sha1/sha1.go      | 110 ++++++++++++++++++++++++++++++++++++++
 hashing/sha1/sha1_test.go |  42 +++++++++++++++
 2 files changed, 152 insertions(+)
 create mode 100644 hashing/sha1/sha1.go
 create mode 100644 hashing/sha1/sha1_test.go

diff --git a/hashing/sha1/sha1.go b/hashing/sha1/sha1.go
new file mode 100644
index 000000000..ba30fe615
--- /dev/null
+++ b/hashing/sha1/sha1.go
@@ -0,0 +1,110 @@
+// sha1.go
+// description: The SHA-1 hashing function as defined in RFC 3174.
+// author: Simon Waldherr
+// ref: https://datatracker.ietf.org/doc/html/rfc3174
+// see sha1_test.go for testing
+
+package sha1
+
+import (
+	"encoding/binary" // Used for interacting with uint at the byte level
+)
+
+// Constants for SHA-1
+const (
+	h0 uint32 = 0x67452301
+	h1 uint32 = 0xEFCDAB89
+	h2 uint32 = 0x98BADCFE
+	h3 uint32 = 0x10325476
+	h4 uint32 = 0xC3D2E1F0
+)
+
+// pad pads the input message so that its length is congruent to 448 modulo 512
+func pad(message []byte) []byte {
+	originalLength := len(message) * 8
+	message = append(message, 0x80)
+	for (len(message)*8)%512 != 448 {
+		message = append(message, 0x00)
+	}
+
+	lengthBytes := make([]byte, 8)
+	binary.BigEndian.PutUint64(lengthBytes, uint64(originalLength))
+	message = append(message, lengthBytes...)
+
+	return message
+}
+
+// leftRotate rotates x left by n bits
+func leftRotate(x, n uint32) uint32 {
+	return (x << n) | (x >> (32 - n))
+}
+
+// Hash computes the SHA-1 hash of the input message
+func Hash(message []byte) [20]byte {
+	message = pad(message)
+
+	// Initialize variables
+	a, b, c, d, e := h0, h1, h2, h3, h4
+
+	// Process the message in successive 512-bit chunks
+	for i := 0; i < len(message); i += 64 {
+		var w [80]uint32
+		chunk := message[i : i+64]
+
+		// Break chunk into sixteen 32-bit big-endian words
+		for j := 0; j < 16; j++ {
+			w[j] = binary.BigEndian.Uint32(chunk[j*4 : (j+1)*4])
+		}
+
+		// Extend the sixteen 32-bit words into eighty 32-bit words
+		for j := 16; j < 80; j++ {
+			w[j] = leftRotate(w[j-3]^w[j-8]^w[j-14]^w[j-16], 1)
+		}
+
+		// Initialize hash value for this chunk
+		A, B, C, D, E := a, b, c, d, e
+
+		// Main loop
+		for j := 0; j < 80; j++ {
+			var f, k uint32
+			switch {
+			case j < 20:
+				f = (B & C) | ((^B) & D)
+				k = 0x5A827999
+			case j < 40:
+				f = B ^ C ^ D
+				k = 0x6ED9EBA1
+			case j < 60:
+				f = (B & C) | (B & D) | (C & D)
+				k = 0x8F1BBCDC
+			default:
+				f = B ^ C ^ D
+				k = 0xCA62C1D6
+			}
+
+			temp := leftRotate(A, 5) + f + E + k + w[j]
+			E = D
+			D = C
+			C = leftRotate(B, 30)
+			B = A
+			A = temp
+		}
+
+		// Add this chunk's hash to result so far
+		a += A
+		b += B
+		c += C
+		d += D
+		e += E
+	}
+
+	// Produce the final hash value (digest)
+	var digest [20]byte
+	binary.BigEndian.PutUint32(digest[0:4], a)
+	binary.BigEndian.PutUint32(digest[4:8], b)
+	binary.BigEndian.PutUint32(digest[8:12], c)
+	binary.BigEndian.PutUint32(digest[12:16], d)
+	binary.BigEndian.PutUint32(digest[16:20], e)
+
+	return digest
+}
diff --git a/hashing/sha1/sha1_test.go b/hashing/sha1/sha1_test.go
new file mode 100644
index 000000000..f7d1d2079
--- /dev/null
+++ b/hashing/sha1/sha1_test.go
@@ -0,0 +1,42 @@
+// sha1_test.go
+// description: Tests for the SHA-1 hashing function as defined in RFC 3174.
+// author: Simon Waldherr
+
+package sha1
+
+import (
+	"encoding/hex"
+	"testing"
+)
+
+// Helper function to convert hash output to hex string for comparison
+func toHexString(hash [20]byte) string {
+	return hex.EncodeToString(hash[:])
+}
+
+// Test vectors for SHA-1 (from RFC 3174 and other known sources)
+var tests = []struct {
+	input    string
+	expected string
+}{
+	{"", "da39a3ee5e6b4b0d3255bfef95601890afd80709"},
+	{"a", "86f7e437faa5a7fce15d1ddcb9eaeaea377667b8"},
+	{"abc", "a9993e364706816aba3e25717850c26c9cd0d89d"},
+	{"message digest", "c12252ceda8be8994d5fa0290a47231c1d16aae3"},
+	{"abcdefghijklmnopqrstuvwxyz", "32d10c7b8cf96570ca04ce37f2a19d84240d3a89"},
+	{"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789", "761c457bf73b14d27e9e9265c46f4b4dda11f940"},
+	{"1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890", "fecfd28bbc9345891a66d7c1b8ff46e60192d284"},
+}
+
+// TestHash verifies that the Hash function produces the correct SHA-1 hash values
+func TestHash(t *testing.T) {
+	for _, tt := range tests {
+		t.Run(tt.input, func(t *testing.T) {
+			result := Hash([]byte(tt.input))
+			resultHex := toHexString(result)
+			if resultHex != tt.expected {
+				t.Errorf("SHA-1(%q) = %s; want %s", tt.input, resultHex, tt.expected)
+			}
+		})
+	}
+}