lib: add crypt subsystem

Add the basic functionality required to support the standard crypt
format.
The files crypt-sha256.c and crypt-sha512.c originate from libxcrypt and
their formatting is therefor retained.
The integration is done via a crypt_compare() function in crypt.c.

```
libxcrypt $ git describe --long --always --all
tags/v4.4.17-0-g6b110bc
```

Signed-off-by: Steffen Jaeckel <jaeckel-floss@eyet-services.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Heiko Schocher <hs@denx.de>

10 files changed, 813 insertions, 0 deletions

diff --git a/lib/Kconfig b/lib/Kconfig
index ad0cd52edd..ad4d75e0a4 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -297,6 +297,7 @@ config AES
 
 source lib/rsa/Kconfig
 source lib/crypto/Kconfig
+source lib/crypt/Kconfig
 
 config TPM
 	bool "Trusted Platform Module (TPM) Support"
diff --git a/lib/Makefile b/lib/Makefile
index d8055d36d6..5cd0c9c638 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -65,6 +65,7 @@ obj-$(CONFIG_HASH) += hash-checksum.o
 obj-$(CONFIG_SHA1) += sha1.o
 obj-$(CONFIG_SHA256) += sha256.o
 obj-$(CONFIG_SHA512_ALGO) += sha512.o
+obj-$(CONFIG_CRYPT_PW) += crypt/
 
 obj-$(CONFIG_$(SPL_)ZLIB) += zlib/
 obj-$(CONFIG_$(SPL_)ZSTD) += zstd/
diff --git a/lib/crypt/Kconfig b/lib/crypt/Kconfig
new file mode 100644
index 0000000000..5495ae8d4c
--- /dev/null
+++ b/lib/crypt/Kconfig
@@ -0,0 +1,28 @@
+menuconfig CRYPT_PW
+	bool "Add crypt support for password-based unlock"
+	depends on AUTOBOOT_KEYED && AUTOBOOT_ENCRYPTION
+	help
+	  Enable support for crypt-style hashed passphrases.
+	  This will then be used as the mechanism of choice to
+	  verify whether the entered password to unlock the
+	  console is correct or not.
+
+if CRYPT_PW
+
+config CRYPT_PW_SHA256
+	bool "Provide sha256crypt"
+	select SHA256
+	select SHA256_ALGO
+	help
+	  Enables support for the sha256crypt password-hashing algorithm.
+	  The prefix is "$5$".
+
+config CRYPT_PW_SHA512
+	bool "Provide sha512crypt"
+	select SHA512
+	select SHA512_ALGO
+	help
+	  Enables support for the sha512crypt password-hashing algorithm.
+	  The prefix is "$6$".
+
+endif
diff --git a/lib/crypt/Makefile b/lib/crypt/Makefile
new file mode 100644
index 0000000000..d53b72b0c7
--- /dev/null
+++ b/lib/crypt/Makefile
@@ -0,0 +1,7 @@
+# SPDX-License-Identifier: GPL-2.0+
+#
+# Copyright (c) 2021, Steffen Jaeckel <jaeckel-floss@eyet-services.de>
+
+obj-$(CONFIG_CRYPT_PW) += crypt.o
+obj-$(CONFIG_CRYPT_PW_SHA256) += crypt-sha256.o
+obj-$(CONFIG_CRYPT_PW_SHA512) += crypt-sha512.o
diff --git a/lib/crypt/alg-sha256.h b/lib/crypt/alg-sha256.h
new file mode 100644
index 0000000000..e4b29c9f31
--- /dev/null
+++ b/lib/crypt/alg-sha256.h
@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/* Copyright (C) 2020 Steffen Jaeckel <jaeckel-floss@eyet-services.de> */
+
+#ifndef USE_HOSTCC
+#include "common.h"
+#else
+#include <string.h>
+#endif
+
+#include "u-boot/sha256.h"
+
+#define INCLUDE_sha256crypt 1
+
+#define SHA256_CTX sha256_context
+#define SHA256_Init sha256_starts
+#define SHA256_Update(c, i, l) sha256_update(c, (const void *)i, l)
+#define SHA256_Final(b, c) sha256_finish(c, b)
diff --git a/lib/crypt/alg-sha512.h b/lib/crypt/alg-sha512.h
new file mode 100644
index 0000000000..93b6109fae
--- /dev/null
+++ b/lib/crypt/alg-sha512.h
@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/* Copyright (C) 2020 Steffen Jaeckel <jaeckel-floss@eyet-services.de> */
+
+#ifndef USE_HOSTCC
+#include "common.h"
+#else
+#include <string.h>
+#endif
+
+#include "u-boot/sha512.h"
+
+#define INCLUDE_sha512crypt 1
+
+#define SHA512_CTX sha512_context
+#define SHA512_Init sha512_starts
+#define SHA512_Update(c, i, l) sha512_update(c, (const void *)i, l)
+#define SHA512_Final(b, c) sha512_finish(c, b)
diff --git a/lib/crypt/crypt-port.h b/lib/crypt/crypt-port.h
new file mode 100644
index 0000000000..680ffe9349
--- /dev/null
+++ b/lib/crypt/crypt-port.h
@@ -0,0 +1,28 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/* Copyright (C) 2020 Steffen Jaeckel <jaeckel-floss@eyet-services.de> */
+
+#include <linux/types.h>
+#include <vsprintf.h>
+
+#define NO_GENSALT
+#define CRYPT_OUTPUT_SIZE 384
+#define ALG_SPECIFIC_SIZE 8192
+
+#define ARG_UNUSED(x) (x)
+
+#define static_assert(a, b) _Static_assert(a, b)
+
+#define strtoul(cp, endp, base) simple_strtoul(cp, endp, base)
+
+extern const unsigned char ascii64[65];
+
+#define b64t ((const char *)ascii64)
+
+void crypt_sha256crypt_rn(const char *phrase, size_t phr_size,
+			  const char *setting, size_t ARG_UNUSED(set_size),
+			  uint8_t *output, size_t out_size, void *scratch,
+			  size_t scr_size);
+void crypt_sha512crypt_rn(const char *phrase, size_t phr_size,
+			  const char *setting, size_t ARG_UNUSED(set_size),
+			  uint8_t *output, size_t out_size, void *scratch,
+			  size_t scr_size);
diff --git a/lib/crypt/crypt-sha256.c b/lib/crypt/crypt-sha256.c
new file mode 100644
index 0000000000..37127d41e1
--- /dev/null
+++ b/lib/crypt/crypt-sha256.c
@@ -0,0 +1,313 @@
+/* One way encryption based on the SHA256-based Unix crypt implementation.
+ *
+ * Written by Ulrich Drepper <drepper at redhat.com> in 2007 [1].
+ * Modified by Zack Weinberg <zackw at panix.com> in 2017, 2018.
+ * Composed by Björn Esser <besser82 at fedoraproject.org> in 2018.
+ * Modified by Björn Esser <besser82 at fedoraproject.org> in 2020.
+ * Modified by Steffen Jaeckel <jaeckel-floss at eyet-services.de> in 2020.
+ * To the extent possible under law, the named authors have waived all
+ * copyright and related or neighboring rights to this work.
+ *
+ * See https://creativecommons.org/publicdomain/zero/1.0/ for further
+ * details.
+ *
+ * This file is a modified except from [2], lines 648 up to 909.
+ *
+ * [1]  https://www.akkadia.org/drepper/sha-crypt.html
+ * [2]  https://www.akkadia.org/drepper/SHA-crypt.txt
+ */
+
+#include "crypt-port.h"
+#include "alg-sha256.h"
+
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#if INCLUDE_sha256crypt
+
+/* 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
+
+/* The maximum possible length of a SHA256-hashed password string,
+   including the terminating NUL character.  Prefix (including its NUL)
+   + rounds tag ("rounds=$" = "rounds=\0") + strlen(ROUNDS_MAX)
+   + salt (up to SALT_LEN_MAX chars) + '$' + hash (43 chars).  */
+
+#define LENGTH_OF_NUMBER(n) (sizeof #n - 1)
+
+#define SHA256_HASH_LENGTH \
+  (sizeof (sha256_salt_prefix) + sizeof (sha256_rounds_prefix) + \
+   LENGTH_OF_NUMBER (ROUNDS_MAX) + SALT_LEN_MAX + 1 + 43)
+
+static_assert (SHA256_HASH_LENGTH <= CRYPT_OUTPUT_SIZE,
+               "CRYPT_OUTPUT_SIZE is too small for SHA256");
+
+/* A sha256_buffer holds all of the sensitive intermediate data.  */
+struct sha256_buffer
+{
+  SHA256_CTX ctx;
+  uint8_t result[32];
+  uint8_t p_bytes[32];
+  uint8_t s_bytes[32];
+};
+
+static_assert (sizeof (struct sha256_buffer) <= ALG_SPECIFIC_SIZE,
+               "ALG_SPECIFIC_SIZE is too small for SHA256");
+
+
+/* Feed CTX with LEN bytes of a virtual byte sequence consisting of
+   BLOCK repeated over and over indefinitely.  */
+static void
+SHA256_Update_recycled (SHA256_CTX *ctx,
+                        unsigned char block[32], size_t len)
+{
+  size_t cnt;
+  for (cnt = len; cnt >= 32; cnt -= 32)
+    SHA256_Update (ctx, block, 32);
+  SHA256_Update (ctx, block, cnt);
+}
+
+void
+crypt_sha256crypt_rn (const char *phrase, size_t phr_size,
+                      const char *setting, size_t ARG_UNUSED (set_size),
+                      uint8_t *output, size_t out_size,
+                      void *scratch, size_t scr_size)
+{
+  /* This shouldn't ever happen, but...  */
+  if (out_size < SHA256_HASH_LENGTH
+      || scr_size < sizeof (struct sha256_buffer))
+    {
+      errno = ERANGE;
+      return;
+    }
+
+  struct sha256_buffer *buf = scratch;
+  SHA256_CTX *ctx = &buf->ctx;
+  uint8_t *result = buf->result;
+  uint8_t *p_bytes = buf->p_bytes;
+  uint8_t *s_bytes = buf->s_bytes;
+  char *cp = (char *)output;
+  const char *salt = setting;
+
+  size_t salt_size;
+  size_t cnt;
+  /* 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;
+      /* Do not allow an explicit setting of zero rounds, nor of the
+         default number of rounds, nor leading zeroes on the rounds.  */
+      if (!(*num >= '1' && *num <= '9'))
+        {
+          errno = EINVAL;
+          return;
+        }
+
+      errno = 0;
+      char *endp;
+      rounds = strtoul (num, &endp, 10);
+      if (endp == num || *endp != '$'
+          || rounds < ROUNDS_MIN
+          || rounds > ROUNDS_MAX
+          || errno)
+        {
+          errno = EINVAL;
+          return;
+        }
+      salt = endp + 1;
+      rounds_custom = true;
+    }
+
+  /* The salt ends at the next '$' or the end of the string.
+     Ensure ':' does not appear in the salt (it is used as a separator in /etc/passwd).
+     Also check for '\n', as in /etc/passwd the whole parameters of the user data must
+     be on a single line. */
+  salt_size = strcspn (salt, "$:\n");
+  if (!(salt[salt_size] == '$' || !salt[salt_size]))
+    {
+      errno = EINVAL;
+      return;
+    }
+
+  /* Ensure we do not use more salt than SALT_LEN_MAX. */
+  if (salt_size > SALT_LEN_MAX)
+    salt_size = SALT_LEN_MAX;
+
+  /* Compute alternate SHA256 sum with input PHRASE, SALT, and PHRASE.  The
+     final result will be added to the first context.  */
+  SHA256_Init (ctx);
+
+  /* Add phrase.  */
+  SHA256_Update (ctx, phrase, phr_size);
+
+  /* Add salt.  */
+  SHA256_Update (ctx, salt, salt_size);
+
+  /* Add phrase again.  */
+  SHA256_Update (ctx, phrase, phr_size);
+
+  /* Now get result of this (32 bytes).  */
+  SHA256_Final (result, ctx);
+
+  /* Prepare for the real work.  */
+  SHA256_Init (ctx);
+
+  /* Add the phrase string.  */
+  SHA256_Update (ctx, phrase, phr_size);
+
+  /* The last part is the salt string.  This must be at most 8
+     characters and it ends at the first `$' character (for
+     compatibility with existing implementations).  */
+  SHA256_Update (ctx, salt, salt_size);
+
+  /* Add for any character in the phrase one byte of the alternate sum.  */
+  for (cnt = phr_size; cnt > 32; cnt -= 32)
+    SHA256_Update (ctx, result, 32);
+  SHA256_Update (ctx, result, cnt);
+
+  /* Take the binary representation of the length of the phrase and for every
+     1 add the alternate sum, for every 0 the phrase.  */
+  for (cnt = phr_size; cnt > 0; cnt >>= 1)
+    if ((cnt & 1) != 0)
+      SHA256_Update (ctx, result, 32);
+    else
+      SHA256_Update (ctx, phrase, phr_size);
+
+  /* Create intermediate result.  */
+  SHA256_Final (result, ctx);
+
+  /* Start computation of P byte sequence.  */
+  SHA256_Init (ctx);
+
+  /* For every character in the password add the entire password.  */
+  for (cnt = 0; cnt < phr_size; ++cnt)
+    SHA256_Update (ctx, phrase, phr_size);
+
+  /* Finish the digest.  */
+  SHA256_Final (p_bytes, ctx);
+
+  /* Start computation of S byte sequence.  */
+  SHA256_Init (ctx);
+
+  /* For every character in the password add the entire password.  */
+  for (cnt = 0; cnt < (size_t) 16 + (size_t) result[0]; ++cnt)
+    SHA256_Update (ctx, salt, salt_size);
+
+  /* Finish the digest.  */
+  SHA256_Final (s_bytes, ctx);
+
+  /* Repeatedly run the collected hash value through SHA256 to burn
+     CPU cycles.  */
+  for (cnt = 0; cnt < rounds; ++cnt)
+    {
+      /* New context.  */
+      SHA256_Init (ctx);
+
+      /* Add phrase or last result.  */
+      if ((cnt & 1) != 0)
+        SHA256_Update_recycled (ctx, p_bytes, phr_size);
+      else
+        SHA256_Update (ctx, result, 32);
+
+      /* Add salt for numbers not divisible by 3.  */
+      if (cnt % 3 != 0)
+        SHA256_Update_recycled (ctx, s_bytes, salt_size);
+
+      /* Add phrase for numbers not divisible by 7.  */
+      if (cnt % 7 != 0)
+        SHA256_Update_recycled (ctx, p_bytes, phr_size);
+
+      /* Add phrase or last result.  */
+      if ((cnt & 1) != 0)
+        SHA256_Update (ctx, result, 32);
+      else
+        SHA256_Update_recycled (ctx, p_bytes, phr_size);
+
+      /* Create intermediate result.  */
+      SHA256_Final (result, ctx);
+    }
+
+  /* Now we can construct the result string.  It consists of four
+     parts, one of which is optional.  We already know that there
+     is sufficient space at CP for the longest possible result string.  */
+  memcpy (cp, sha256_salt_prefix, sizeof (sha256_salt_prefix) - 1);
+  cp += sizeof (sha256_salt_prefix) - 1;
+
+  if (rounds_custom)
+    {
+      int n = snprintf (cp,
+                        SHA256_HASH_LENGTH - (sizeof (sha256_salt_prefix) - 1),
+                        "%s%zu$", sha256_rounds_prefix, rounds);
+      cp += n;
+    }
+
+  memcpy (cp, salt, salt_size);
+  cp += salt_size;
+  *cp++ = '$';
+
+#define b64_from_24bit(B2, B1, B0, N)                   \
+  do {                                                  \
+    unsigned int w = ((((unsigned int)(B2)) << 16) |    \
+                      (((unsigned int)(B1)) << 8) |     \
+                      ((unsigned int)(B0)));            \
+    int n = (N);                                        \
+    while (n-- > 0)                                     \
+      {                                                 \
+        *cp++ = b64t[w & 0x3f];                         \
+        w >>= 6;                                        \
+      }                                                 \
+  } while (0)
+
+  b64_from_24bit (result[0], result[10], result[20], 4);
+  b64_from_24bit (result[21], result[1], result[11], 4);
+  b64_from_24bit (result[12], result[22], result[2], 4);
+  b64_from_24bit (result[3], result[13], result[23], 4);
+  b64_from_24bit (result[24], result[4], result[14], 4);
+  b64_from_24bit (result[15], result[25], result[5], 4);
+  b64_from_24bit (result[6], result[16], result[26], 4);
+  b64_from_24bit (result[27], result[7], result[17], 4);
+  b64_from_24bit (result[18], result[28], result[8], 4);
+  b64_from_24bit (result[9], result[19], result[29], 4);
+  b64_from_24bit (0, result[31], result[30], 3);
+
+  *cp = '\0';
+}
+
+#ifndef NO_GENSALT
+
+void
+gensalt_sha256crypt_rn (unsigned long count,
+                        const uint8_t *rbytes, size_t nrbytes,
+                        uint8_t *output, size_t output_size)
+{
+  gensalt_sha_rn ('5', SALT_LEN_MAX, ROUNDS_DEFAULT, ROUNDS_MIN, ROUNDS_MAX,
+                  count, rbytes, nrbytes, output, output_size);
+}
+
+#endif
+
+#endif
diff --git a/lib/crypt/crypt-sha512.c b/lib/crypt/crypt-sha512.c
new file mode 100644
index 0000000000..3616019445
--- /dev/null
+++ b/lib/crypt/crypt-sha512.c
@@ -0,0 +1,328 @@
+/* One way encryption based on the SHA512-based Unix crypt implementation.
+ *
+ * Written by Ulrich Drepper <drepper at redhat.com> in 2007 [1].
+ * Modified by Zack Weinberg <zackw at panix.com> in 2017, 2018.
+ * Composed by Björn Esser <besser82 at fedoraproject.org> in 2018.
+ * Modified by Björn Esser <besser82 at fedoraproject.org> in 2020.
+ * Modified by Steffen Jaeckel <jaeckel-floss at eyet-services.de> in 2020.
+ * To the extent possible under law, the named authors have waived all
+ * copyright and related or neighboring rights to this work.
+ *
+ * See https://creativecommons.org/publicdomain/zero/1.0/ for further
+ * details.
+ *
+ * This file is a modified except from [2], lines 1403 up to 1676.
+ *
+ * [1]  https://www.akkadia.org/drepper/sha-crypt.html
+ * [2]  https://www.akkadia.org/drepper/SHA-crypt.txt
+ */
+
+#include "crypt-port.h"
+#include "alg-sha512.h"
+
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#if INCLUDE_sha512crypt
+
+/* Define our magic string to mark salt for SHA512 "encryption"
+   replacement.  */
+static const char sha512_salt_prefix[] = "$6$";
+
+/* Prefix for optional rounds specification.  */
+static const char sha512_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
+
+/* The maximum possible length of a SHA512-hashed password string,
+   including the terminating NUL character.  Prefix (including its NUL)
+   + rounds tag ("rounds=$" = "rounds=\0") + strlen(ROUNDS_MAX)
+   + salt (up to SALT_LEN_MAX chars) + '$' + hash (86 chars).  */
+
+#define LENGTH_OF_NUMBER(n) (sizeof #n - 1)
+
+#define SHA512_HASH_LENGTH \
+  (sizeof (sha512_salt_prefix) + sizeof (sha512_rounds_prefix) + \
+   LENGTH_OF_NUMBER (ROUNDS_MAX) + SALT_LEN_MAX + 1 + 86)
+
+static_assert (SHA512_HASH_LENGTH <= CRYPT_OUTPUT_SIZE,
+               "CRYPT_OUTPUT_SIZE is too small for SHA512");
+
+/* A sha512_buffer holds all of the sensitive intermediate data.  */
+struct sha512_buffer
+{
+  SHA512_CTX ctx;
+  uint8_t result[64];
+  uint8_t p_bytes[64];
+  uint8_t s_bytes[64];
+};
+
+static_assert (sizeof (struct sha512_buffer) <= ALG_SPECIFIC_SIZE,
+               "ALG_SPECIFIC_SIZE is too small for SHA512");
+
+
+/* Subroutine of _xcrypt_crypt_sha512crypt_rn: Feed CTX with LEN bytes of a
+   virtual byte sequence consisting of BLOCK repeated over and over
+   indefinitely.  */
+static void
+sha512_process_recycled_bytes (unsigned char block[64], size_t len,
+                               SHA512_CTX *ctx)
+{
+  size_t cnt;
+  for (cnt = len; cnt >= 64; cnt -= 64)
+    SHA512_Update (ctx, block, 64);
+  SHA512_Update (ctx, block, cnt);
+}
+
+void
+crypt_sha512crypt_rn (const char *phrase, size_t phr_size,
+                      const char *setting, size_t ARG_UNUSED (set_size),
+                      uint8_t *output, size_t out_size,
+                      void *scratch, size_t scr_size)
+{
+  /* This shouldn't ever happen, but...  */
+  if (out_size < SHA512_HASH_LENGTH
+      || scr_size < sizeof (struct sha512_buffer))
+    {
+      errno = ERANGE;
+      return;
+    }
+
+  struct sha512_buffer *buf = scratch;
+  SHA512_CTX *ctx = &buf->ctx;
+  uint8_t *result = buf->result;
+  uint8_t *p_bytes = buf->p_bytes;
+  uint8_t *s_bytes = buf->s_bytes;
+  char *cp = (char *)output;
+  const char *salt = setting;
+
+  size_t salt_size;
+  size_t cnt;
+  /* 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 (sha512_salt_prefix, salt, sizeof (sha512_salt_prefix) - 1) == 0)
+    /* Skip salt prefix.  */
+    salt += sizeof (sha512_salt_prefix) - 1;
+
+  if (strncmp (salt, sha512_rounds_prefix, sizeof (sha512_rounds_prefix) - 1)
+      == 0)
+    {
+      const char *num = salt + sizeof (sha512_rounds_prefix) - 1;
+      /* Do not allow an explicit setting of zero rounds, nor of the
+         default number of rounds, nor leading zeroes on the rounds.  */
+      if (!(*num >= '1' && *num <= '9'))
+        {
+          errno = EINVAL;
+          return;
+        }
+
+      errno = 0;
+      char *endp;
+      rounds = strtoul (num, &endp, 10);
+      if (endp == num || *endp != '$'
+          || rounds < ROUNDS_MIN
+          || rounds > ROUNDS_MAX
+          || errno)
+        {
+          errno = EINVAL;
+          return;
+        }
+      salt = endp + 1;
+      rounds_custom = true;
+    }
+
+  /* The salt ends at the next '$' or the end of the string.
+     Ensure ':' does not appear in the salt (it is used as a separator in /etc/passwd).
+     Also check for '\n', as in /etc/passwd the whole parameters of the user data must
+     be on a single line. */
+  salt_size = strcspn (salt, "$:\n");
+  if (!(salt[salt_size] == '$' || !salt[salt_size]))
+    {
+      errno = EINVAL;
+      return;
+    }
+
+  /* Ensure we do not use more salt than SALT_LEN_MAX. */
+  if (salt_size > SALT_LEN_MAX)
+    salt_size = SALT_LEN_MAX;
+
+  /* Compute alternate SHA512 sum with input PHRASE, SALT, and PHRASE.  The
+     final result will be added to the first context.  */
+  SHA512_Init (ctx);
+
+  /* Add phrase.  */
+  SHA512_Update (ctx, phrase, phr_size);
+
+  /* Add salt.  */
+  SHA512_Update (ctx, salt, salt_size);
+
+  /* Add phrase again.  */
+  SHA512_Update (ctx, phrase, phr_size);
+
+  /* Now get result of this (64 bytes) and add it to the other
+     context.  */
+  SHA512_Final (result, ctx);
+
+  /* Prepare for the real work.  */
+  SHA512_Init (ctx);
+
+  /* Add the phrase string.  */
+  SHA512_Update (ctx, phrase, phr_size);
+
+  /* The last part is the salt string.  This must be at most 8
+     characters and it ends at the first `$' character (for
+     compatibility with existing implementations).  */
+  SHA512_Update (ctx, salt, salt_size);
+
+  /* Add for any character in the phrase one byte of the alternate sum.  */
+  for (cnt = phr_size; cnt > 64; cnt -= 64)
+    SHA512_Update (ctx, result, 64);
+  SHA512_Update (ctx, result, cnt);
+
+  /* Take the binary representation of the length of the phrase and for every
+     1 add the alternate sum, for every 0 the phrase.  */
+  for (cnt = phr_size; cnt > 0; cnt >>= 1)
+    if ((cnt & 1) != 0)
+      SHA512_Update (ctx, result, 64);
+    else
+      SHA512_Update (ctx, phrase, phr_size);
+
+  /* Create intermediate result.  */
+  SHA512_Final (result, ctx);
+
+  /* Start computation of P byte sequence.  */
+  SHA512_Init (ctx);
+
+  /* For every character in the password add the entire password.  */
+  for (cnt = 0; cnt < phr_size; ++cnt)
+    SHA512_Update (ctx, phrase, phr_size);
+
+  /* Finish the digest.  */
+  SHA512_Final (p_bytes, ctx);
+
+  /* Start computation of S byte sequence.  */
+  SHA512_Init (ctx);
+
+  /* For every character in the password add the entire password.  */
+  for (cnt = 0; cnt < (size_t) 16 + (size_t) result[0]; ++cnt)
+    SHA512_Update (ctx, salt, salt_size);
+
+  /* Finish the digest.  */
+  SHA512_Final (s_bytes, ctx);
+
+  /* Repeatedly run the collected hash value through SHA512 to burn
+     CPU cycles.  */
+  for (cnt = 0; cnt < rounds; ++cnt)
+    {
+      /* New context.  */
+      SHA512_Init (ctx);
+
+      /* Add phrase or last result.  */
+      if ((cnt & 1) != 0)
+        sha512_process_recycled_bytes (p_bytes, phr_size, ctx);
+      else
+        SHA512_Update (ctx, result, 64);
+
+      /* Add salt for numbers not divisible by 3.  */
+      if (cnt % 3 != 0)
+        sha512_process_recycled_bytes (s_bytes, salt_size, ctx);
+
+      /* Add phrase for numbers not divisible by 7.  */
+      if (cnt % 7 != 0)
+        sha512_process_recycled_bytes (p_bytes, phr_size, ctx);
+
+      /* Add phrase or last result.  */
+      if ((cnt & 1) != 0)
+        SHA512_Update (ctx, result, 64);
+      else
+        sha512_process_recycled_bytes (p_bytes, phr_size, ctx);
+
+      /* Create intermediate result.  */
+      SHA512_Final (result, ctx);
+    }
+
+  /* Now we can construct the result string.  It consists of four
+     parts, one of which is optional.  We already know that buflen is
+     at least sha512_hash_length, therefore none of the string bashing
+     below can overflow the buffer. */
+
+  memcpy (cp, sha512_salt_prefix, sizeof (sha512_salt_prefix) - 1);
+  cp += sizeof (sha512_salt_prefix) - 1;
+
+  if (rounds_custom)
+    {
+      int n = snprintf (cp,
+                        SHA512_HASH_LENGTH - (sizeof (sha512_salt_prefix) - 1),
+                        "%s%zu$", sha512_rounds_prefix, rounds);
+      cp += n;
+    }
+
+  memcpy (cp, salt, salt_size);
+  cp += salt_size;
+  *cp++ = '$';
+
+#define b64_from_24bit(B2, B1, B0, N)                   \
+  do {                                                  \
+    unsigned int w = ((((unsigned int)(B2)) << 16) |    \
+                      (((unsigned int)(B1)) << 8) |     \
+                      ((unsigned int)(B0)));            \
+    int n = (N);                                        \
+    while (n-- > 0)                                     \
+      {                                                 \
+        *cp++ = b64t[w & 0x3f];                         \
+        w >>= 6;                                        \
+      }                                                 \
+  } while (0)
+
+  b64_from_24bit (result[0], result[21], result[42], 4);
+  b64_from_24bit (result[22], result[43], result[1], 4);
+  b64_from_24bit (result[44], result[2], result[23], 4);
+  b64_from_24bit (result[3], result[24], result[45], 4);
+  b64_from_24bit (result[25], result[46], result[4], 4);
+  b64_from_24bit (result[47], result[5], result[26], 4);
+  b64_from_24bit (result[6], result[27], result[48], 4);
+  b64_from_24bit (result[28], result[49], result[7], 4);
+  b64_from_24bit (result[50], result[8], result[29], 4);
+  b64_from_24bit (result[9], result[30], result[51], 4);
+  b64_from_24bit (result[31], result[52], result[10], 4);
+  b64_from_24bit (result[53], result[11], result[32], 4);
+  b64_from_24bit (result[12], result[33], result[54], 4);
+  b64_from_24bit (result[34], result[55], result[13], 4);
+  b64_from_24bit (result[56], result[14], result[35], 4);
+  b64_from_24bit (result[15], result[36], result[57], 4);
+  b64_from_24bit (result[37], result[58], result[16], 4);
+  b64_from_24bit (result[59], result[17], result[38], 4);
+  b64_from_24bit (result[18], result[39], result[60], 4);
+  b64_from_24bit (result[40], result[61], result[19], 4);
+  b64_from_24bit (result[62], result[20], result[41], 4);
+  b64_from_24bit (0, 0, result[63], 2);
+
+  *cp = '\0';
+}
+
+#ifndef NO_GENSALT
+
+void
+gensalt_sha512crypt_rn (unsigned long count,
+                        const uint8_t *rbytes, size_t nrbytes,
+                        uint8_t *output, size_t output_size)
+{
+  gensalt_sha_rn ('6', SALT_LEN_MAX, ROUNDS_DEFAULT, ROUNDS_MIN, ROUNDS_MAX,
+                  count, rbytes, nrbytes, output, output_size);
+}
+
+#endif
+
+#endif
diff --git a/lib/crypt/crypt.c b/lib/crypt/crypt.c
new file mode 100644
index 0000000000..4ec6079768
--- /dev/null
+++ b/lib/crypt/crypt.c
@@ -0,0 +1,73 @@
+// SPDX-License-Identifier: GPL-2.0+
+/* Copyright (C) 2020 Steffen Jaeckel <jaeckel-floss@eyet-services.de> */
+
+#include <common.h>
+#include <crypt.h>
+#include "crypt-port.h"
+
+typedef void (*crypt_fn)(const char *, size_t, const char *, size_t, uint8_t *,
+			 size_t, void *, size_t);
+
+const unsigned char ascii64[65] =
+	"./0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
+
+static void equals_constant_time(const void *a_, const void *b_, size_t len,
+				 int *equal)
+{
+	u8 ret = 0;
+	const u8 *a = a_, *b = b_;
+	int i;
+
+	for (i = 0; i < len; i++)
+		ret |= a[i] ^ b[i];
+
+	ret |= ret >> 4;
+	ret |= ret >> 2;
+	ret |= ret >> 1;
+	ret &= 1;
+
+	*equal = ret ^ 1;
+}
+
+void crypt_compare(const char *should, const char *passphrase, int *equal)
+{
+	u8 output[CRYPT_OUTPUT_SIZE], scratch[ALG_SPECIFIC_SIZE];
+	size_t n;
+	struct {
+		const char *prefix;
+		crypt_fn crypt;
+	} crypt_algos[] = {
+#if defined(CONFIG_CRYPT_PW_SHA256)
+		{ "$5$", crypt_sha256crypt_rn },
+#endif
+#if defined(CONFIG_CRYPT_PW_SHA512)
+		{ "$6$", crypt_sha512crypt_rn },
+#endif
+		{ NULL, NULL }
+	};
+
+	*equal = 0;
+
+	for (n = 0; n < ARRAY_SIZE(crypt_algos); ++n) {
+		if (!crypt_algos[n].prefix)
+			continue;
+		if (strncmp(should, crypt_algos[n].prefix, 3) == 0)
+			break;
+	}
+
+	if (n >= ARRAY_SIZE(crypt_algos))
+		return;
+
+	crypt_algos[n].crypt(passphrase, strlen(passphrase), should, 0, output,
+			     sizeof(output), scratch, sizeof(scratch));
+
+	/* early return on error, nothing really happened inside the crypt() function */
+	if (errno == ERANGE || errno == EINVAL)
+		return;
+
+	equals_constant_time(should, output, strlen((const char *)output),
+			     equal);
+
+	memset(scratch, 0, sizeof(scratch));
+	memset(output, 0, sizeof(output));
+}