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>

1 files changed, 73 insertions, 0 deletions

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));
+}