libcrypt: add support for SHA256-CRYPT password hashing

This is based on Ulrich Drepper's implementation in GLIBC, but hacked up to work
in uClibc.  The differences from the GLIBC version are as follows:

- b64_from_24bit() has been converted into a macro
- Usage of GLIBC-isms (such as libc_freeres_ptr) have been removed

It is enabled by the UCLIBC_HAS_SHA256_CRYPT_IMPL configuration symbol.  You must
have UCLIBC_HAS_CRYPT_IMPL enabled as well.

Signed-off-by: William Pitcock <nenolod@dereferenced.org>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>

1 files changed, 326 insertions, 0 deletions

diff --git a/libcrypt/sha256-crypt.c b/libcrypt/sha256-crypt.c
new file mode 100644
index 000000000..44221482f
--- /dev/null
+++ b/libcrypt/sha256-crypt.c
@@ -0,0 +1,326 @@
+/* One way encryption based on SHA256 sum.
+   Copyright (C) 2007, 2009 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Ulrich Drepper <drepper@redhat.com>, 2007.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, write to the Free
+   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+   02111-1307 USA.  */
+
+#include <assert.h>
+#include <errno.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/param.h>
+
+#include "sha256.h"
+#include "libcrypt.h"
+
+/* Define our magic string to mark salt for SHA256 "encryption"
+   replacement.  */
+static const char sha256_salt_prefix[] = "$5$";
+
+/* Prefix for optional rounds specification.  */
+static const char sha256_rounds_prefix[] = "rounds=";
+
+/* Maximum salt string length.  */
+#define SALT_LEN_MAX 16
+/* Default number of rounds if not explicitly specified.  */
+#define ROUNDS_DEFAULT 5000
+/* Minimum number of rounds.  */
+#define ROUNDS_MIN 1000
+/* Maximum number of rounds.  */
+#define ROUNDS_MAX 999999999
+
+/* Table with characters for base64 transformation.  */
+static const char b64t[64] =
+"./0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
+
+#define B64_FROM_24BIT(b2, b1, b0, steps) \
+	{ \
+		int n = (steps); \
+		unsigned int w = ((b2) << 16) | ((b1) << 8) | (b0); \
+		while (n-- > 0 && buflen > 0) \
+		{ \
+			*cp++ = b64t[w & 0x3f]; \
+			--buflen; \
+			w >>= 6; \
+		} \
+	}
+
+char *
+__sha256_crypt_r (const char *key,
+     const char *salt,
+     char *buffer,
+     int buflen)
+{
+  unsigned char alt_result[32]
+    __attribute__ ((__aligned__ (__alignof__ (uint32_t))));
+  unsigned char temp_result[32]
+    __attribute__ ((__aligned__ (__alignof__ (uint32_t))));
+  size_t salt_len;
+  size_t key_len;
+  size_t cnt;
+  char *cp;
+  char *copied_key = NULL;
+  char *copied_salt = NULL;
+  char *p_bytes;
+  char *s_bytes;
+  /* Default number of rounds.  */
+  size_t rounds = ROUNDS_DEFAULT;
+  bool rounds_custom = false;
+
+  /* Find beginning of salt string.  The prefix should normally always
+     be present.  Just in case it is not.  */
+  if (strncmp (sha256_salt_prefix, salt, sizeof (sha256_salt_prefix) - 1) == 0)
+    /* Skip salt prefix.  */
+    salt += sizeof (sha256_salt_prefix) - 1;
+
+  if (strncmp (salt, sha256_rounds_prefix, sizeof (sha256_rounds_prefix) - 1)
+      == 0)
+    {
+      const char *num = salt + sizeof (sha256_rounds_prefix) - 1;
+      char *endp;
+      unsigned long int srounds = strtoul (num, &endp, 10);
+      if (*endp == '$')
+	{
+	  salt = endp + 1;
+	  rounds = MAX (ROUNDS_MIN, MIN (srounds, ROUNDS_MAX));
+	  rounds_custom = true;
+	}
+    }
+
+  salt_len = MIN (strcspn (salt, "$"), SALT_LEN_MAX);
+  key_len = strlen (key);
+
+  if ((key - (char *) 0) % __alignof__ (uint32_t) != 0)
+    {
+      char *tmp = (char *) alloca (key_len + __alignof__ (uint32_t));
+      key = copied_key =
+	memcpy (tmp + __alignof__ (uint32_t)
+		- (tmp - (char *) 0) % __alignof__ (uint32_t),
+		key, key_len);
+      assert ((key - (char *) 0) % __alignof__ (uint32_t) == 0);
+    }
+
+  if ((salt - (char *) 0) % __alignof__ (uint32_t) != 0)
+    {
+      char *tmp = (char *) alloca (salt_len + __alignof__ (uint32_t));
+      salt = copied_salt =
+	memcpy (tmp + __alignof__ (uint32_t)
+		- (tmp - (char *) 0) % __alignof__ (uint32_t),
+		salt, salt_len);
+      assert ((salt - (char *) 0) % __alignof__ (uint32_t) == 0);
+    }
+
+  struct sha256_ctx ctx;
+  struct sha256_ctx alt_ctx;
+
+  /* Prepare for the real work.  */
+  __sha256_init_ctx (&ctx);
+
+  /* Add the key string.  */
+  __sha256_process_bytes (key, key_len, &ctx);
+
+  /* The last part is the salt string.  This must be at most 16
+     characters and it ends at the first `$' character.  */
+  __sha256_process_bytes (salt, salt_len, &ctx);
+
+
+  /* Compute alternate SHA256 sum with input KEY, SALT, and KEY.  The
+     final result will be added to the first context.  */
+  __sha256_init_ctx (&alt_ctx);
+
+  /* Add key.  */
+  __sha256_process_bytes (key, key_len, &alt_ctx);
+
+  /* Add salt.  */
+  __sha256_process_bytes (salt, salt_len, &alt_ctx);
+
+  /* Add key again.  */
+  __sha256_process_bytes (key, key_len, &alt_ctx);
+
+  /* Now get result of this (32 bytes) and add it to the other
+     context.  */
+  __sha256_finish_ctx (&alt_ctx, alt_result);
+
+  /* Add for any character in the key one byte of the alternate sum.  */
+  for (cnt = key_len; cnt > 32; cnt -= 32)
+    __sha256_process_bytes (alt_result, 32, &ctx);
+  __sha256_process_bytes (alt_result, cnt, &ctx);
+
+  /* Take the binary representation of the length of the key and for every
+     1 add the alternate sum, for every 0 the key.  */
+  for (cnt = key_len; cnt > 0; cnt >>= 1)
+    if ((cnt & 1) != 0)
+      __sha256_process_bytes (alt_result, 32, &ctx);
+    else
+      __sha256_process_bytes (key, key_len, &ctx);
+
+  /* Create intermediate result.  */
+  __sha256_finish_ctx (&ctx, alt_result);
+
+  /* Start computation of P byte sequence.  */
+  __sha256_init_ctx (&alt_ctx);
+
+  /* For every character in the password add the entire password.  */
+  for (cnt = 0; cnt < key_len; ++cnt)
+    __sha256_process_bytes (key, key_len, &alt_ctx);
+
+  /* Finish the digest.  */
+  __sha256_finish_ctx (&alt_ctx, temp_result);
+
+  /* Create byte sequence P.  */
+  cp = p_bytes = alloca (key_len);
+  for (cnt = key_len; cnt >= 32; cnt -= 32)
+    cp = mempcpy (cp, temp_result, 32);
+  memcpy (cp, temp_result, cnt);
+
+  /* Start computation of S byte sequence.  */
+  __sha256_init_ctx (&alt_ctx);
+
+  /* For every character in the password add the entire password.  */
+  for (cnt = 0; cnt < 16 + alt_result[0]; ++cnt)
+    __sha256_process_bytes (salt, salt_len, &alt_ctx);
+
+  /* Finish the digest.  */
+  __sha256_finish_ctx (&alt_ctx, temp_result);
+
+  /* Create byte sequence S.  */
+  cp = s_bytes = alloca (salt_len);
+  for (cnt = salt_len; cnt >= 32; cnt -= 32)
+    cp = mempcpy (cp, temp_result, 32);
+  memcpy (cp, temp_result, cnt);
+
+  /* Repeatedly run the collected hash value through SHA256 to burn
+     CPU cycles.  */
+  for (cnt = 0; cnt < rounds; ++cnt)
+    {
+      /* New context.  */
+      __sha256_init_ctx (&ctx);
+
+      /* Add key or last result.  */
+      if ((cnt & 1) != 0)
+	__sha256_process_bytes (p_bytes, key_len, &ctx);
+      else
+	__sha256_process_bytes (alt_result, 32, &ctx);
+
+      /* Add salt for numbers not divisible by 3.  */
+      if (cnt % 3 != 0)
+	__sha256_process_bytes (s_bytes, salt_len, &ctx);
+
+      /* Add key for numbers not divisible by 7.  */
+      if (cnt % 7 != 0)
+	__sha256_process_bytes (p_bytes, key_len, &ctx);
+
+      /* Add key or last result.  */
+      if ((cnt & 1) != 0)
+	__sha256_process_bytes (alt_result, 32, &ctx);
+      else
+	__sha256_process_bytes (p_bytes, key_len, &ctx);
+
+      /* Create intermediate result.  */
+      __sha256_finish_ctx (&ctx, alt_result);
+    }
+
+  /* Now we can construct the result string.  It consists of three
+     parts.  */
+  cp = stpncpy (buffer, sha256_salt_prefix, MAX (0, buflen));
+  buflen -= sizeof (sha256_salt_prefix) - 1;
+
+  if (rounds_custom)
+    {
+      int n = snprintf (cp, MAX (0, buflen), "%s%zu$",
+			sha256_rounds_prefix, rounds);
+      cp += n;
+      buflen -= n;
+    }
+
+  cp = stpncpy (cp, salt, MIN ((size_t) MAX (0, buflen), salt_len));
+  buflen -= MIN ((size_t) MAX (0, buflen), salt_len);
+
+  if (buflen > 0)
+    {
+      *cp++ = '$';
+      --buflen;
+    }
+
+  B64_FROM_24BIT (alt_result[0], alt_result[10], alt_result[20], 4);
+  B64_FROM_24BIT (alt_result[21], alt_result[1], alt_result[11], 4);
+  B64_FROM_24BIT (alt_result[12], alt_result[22], alt_result[2], 4);
+  B64_FROM_24BIT (alt_result[3], alt_result[13], alt_result[23], 4);
+  B64_FROM_24BIT (alt_result[24], alt_result[4], alt_result[14], 4);
+  B64_FROM_24BIT (alt_result[15], alt_result[25], alt_result[5], 4);
+  B64_FROM_24BIT (alt_result[6], alt_result[16], alt_result[26], 4);
+  B64_FROM_24BIT (alt_result[27], alt_result[7], alt_result[17], 4);
+  B64_FROM_24BIT (alt_result[18], alt_result[28], alt_result[8], 4);
+  B64_FROM_24BIT (alt_result[9], alt_result[19], alt_result[29], 4);
+  B64_FROM_24BIT (0, alt_result[31], alt_result[30], 3);
+  if (buflen <= 0)
+    {
+      __set_errno (ERANGE);
+      buffer = NULL;
+    }
+  else
+    *cp = '\0';		/* Terminate the string.  */
+
+  /* Clear the buffer for the intermediate result so that people
+     attaching to processes or reading core dumps cannot get any
+     information.  We do it in this way to clear correct_words[]
+     inside the SHA256 implementation as well.  */
+  __sha256_init_ctx (&ctx);
+  __sha256_finish_ctx (&ctx, alt_result);
+  memset (&ctx, '\0', sizeof (ctx));
+  memset (&alt_ctx, '\0', sizeof (alt_ctx));
+
+  memset (temp_result, '\0', sizeof (temp_result));
+  memset (p_bytes, '\0', key_len);
+  memset (s_bytes, '\0', salt_len);
+  if (copied_key != NULL)
+    memset (copied_key, '\0', key_len);
+  if (copied_salt != NULL)
+    memset (copied_salt, '\0', salt_len);
+
+  return buffer;
+}
+
+static char *buffer;
+
+/* This entry point is equivalent to the `crypt' function in Unix
+   libcs.  */
+char *
+__sha256_crypt (const unsigned char *key, const unsigned char *salt)
+{
+  /* We don't want to have an arbitrary limit in the size of the
+     password.  We can compute an upper bound for the size of the
+     result in advance and so we can prepare the buffer we pass to
+     `sha256_crypt_r'.  */
+  static int buflen;
+  int needed = (sizeof (sha256_salt_prefix) - 1
+		+ sizeof (sha256_rounds_prefix) + 9 + 1
+		+ strlen (salt) + 1 + 43 + 1);
+
+  if (buflen < needed)
+    {
+      char *new_buffer = (char *) realloc (buffer, needed);
+      if (new_buffer == NULL)
+	return NULL;
+
+      buffer = new_buffer;
+      buflen = needed;
+    }
+
+  return __sha256_crypt_r ((const char *) key, (const char *) salt, buffer, buflen);
+}