From daf6eeca41a2eef8e07355824dc647e566c2832f Mon Sep 17 00:00:00 2001
From: Nick Chambers <uplime@spookyinternet.com>
Date: Sun, 25 Jul 2021 20:37:10 -0500
Subject: [PATCH] c/sha1.c: SHA1 hashing algorithm implementation

---
 c/sha1.c | 137 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 137 insertions(+)
 create mode 100644 c/sha1.c

diff --git a/c/sha1.c b/c/sha1.c
new file mode 100644
index 0000000..9ba14d0
--- /dev/null
+++ b/c/sha1.c
@@ -0,0 +1,137 @@
+#include <limits.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+static uint64_t pad_length(uint64_t len) {
+  uint64_t space_needed = 1;
+
+  while(((len + space_needed) % 64) != 56) {
+    space_needed += 1;
+  }
+    
+  return space_needed;
+}
+
+static uint32_t rotate(uint8_t bits, uint32_t word) {
+  return (word << bits) | (word >> (32 - bits));
+}
+
+unsigned char *sha1(const char *msg, uint64_t len) {
+  uint64_t ml = len * CHAR_BIT;
+  uint64_t needed = pad_length(len);
+  unsigned char *buf = malloc(len + needed + 8);
+
+  if(buf == NULL) {
+    return NULL;
+  }
+
+  strncpy((char *) buf, msg, len);
+  buf[len++] = 0x80;
+
+  for(; needed > 1; --needed) {
+    buf[len++] = 0x00;
+  }
+
+  uint8_t count = 8;
+
+  while(count--) {
+    buf[len++] = (ml & ((uint64_t) 0xFF << 56)) >> 56;
+    ml = ml << 8;
+  }
+
+  uint32_t h[] = {
+    0x67452301,
+    0xEFCDAB89,
+    0x98BADCFE,
+    0x10325476,
+    0xC3D2E1F0
+  };
+
+  uint64_t chunk = 0;
+
+  for(; chunk < len; chunk += 64) {
+    uint32_t w[80] = { 0 };
+    uint8_t i = 0;
+
+    for(; i < 16; i++) {
+      w[i] = buf[chunk + (i * 4)] << 24;
+      w[i] |= buf[chunk + (i * 4 + 1)] << 16;
+      w[i] |= buf[chunk + (i * 4 + 2)] << 8;
+      w[i] |= buf[chunk + (i * 4 + 3)];
+    }
+
+    for(i = 16; i < 80; ++i) {
+      w[i] = rotate(1, w[i - 3] ^ w[i - 8] ^ w[i - 14] ^ w[i - 16]);
+    }
+
+    uint32_t a = h[0];
+    uint32_t b = h[1];
+    uint32_t c = h[2];
+    uint32_t d = h[3];
+    uint32_t e = h[4];
+
+    for(i = 0; i < 80; ++i) {
+      uint32_t f = 0;
+      uint32_t k = 0;
+ 
+      if(i >= 0 && i <= 19) {
+        f = (b & c) | ((~b) & d);
+        k = (uint32_t) 0x5A827999;
+      } else if(i >= 20 && i <= 39) {
+        f = b ^ c ^ d;
+        k = (uint32_t) 0x6ED9EBA1;
+      } else if(i >= 40 && i <= 59) {
+        f = (b & c) | (b & d) | (c & d);
+        k = (uint32_t) 0x8F1BBCDC;
+      } else if(i >= 60 && i <= 79) {
+        f = b ^ c ^ d;
+        k = (uint32_t) 0xCA62C1D6;
+      }
+ 
+      uint32_t temp = rotate(5, a) + f + e + k + w[i];
+      e = d;
+      d = c;
+      c = rotate(30, b);
+      b = a;
+      a = temp;
+    }
+
+    h[0] += a;
+    h[1] += b;
+    h[2] += c;
+    h[3] += d;
+    h[4] += e;
+  }
+
+  unsigned char *hh = malloc(20);
+
+  if(hh == NULL) {
+    return NULL;
+  }
+
+  for(count = 0; count < 5; count++) {
+    hh[count * 4] = h[count] >> 24;
+    hh[(count * 4) + 1] = (h[count] >> 16) & 0xFF;
+    hh[(count * 4) + 2] = (h[count] >> 8) & 0xFF;
+    hh[(count * 4) + 3] = h[count] & 0xFF;
+  }
+
+  return hh;
+}
+
+int main(int argc, char **argv) {
+  for(++argv; argc > 1; ++argv, --argc) {
+    unsigned char *hash = sha1(*argv, strlen(*argv));
+    uint8_t count = 0;
+
+    for(; count < 20; ++count) {
+      printf("%02X", (unsigned) hash[count]);
+    }
+
+    printf("\n");
+  }
+
+  return 0;
+}