NetworkManager/libnm-core/crypto.c

/* -*- Mode: C; tab-width: 4; indent-tabs-mode: t; c-basic-offset: 4 -*- */

/*
 * Dan Williams <dcbw@redhat.com>
 *
 * This 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 of the License, or (at your option) any later version.
 *
 * This 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 this library; if not, write to the
 * Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
 * Boston, MA 02110-1301 USA.
 *
 * Copyright 2007 - 2011 Red Hat, Inc.
 */

#include "nm-default.h"

#include <string.h>
#include <strings.h>
#include <unistd.h>
#include <stdlib.h>

#include "crypto.h"
#include "nm-errors.h"

#define PEM_RSA_KEY_BEGIN "-----BEGIN RSA PRIVATE KEY-----"
#define PEM_RSA_KEY_END   "-----END RSA PRIVATE KEY-----"

#define PEM_DSA_KEY_BEGIN "-----BEGIN DSA PRIVATE KEY-----"
#define PEM_DSA_KEY_END   "-----END DSA PRIVATE KEY-----"

#define PEM_CERT_BEGIN    "-----BEGIN CERTIFICATE-----"
#define PEM_CERT_END      "-----END CERTIFICATE-----"

#define PEM_PKCS8_ENC_KEY_BEGIN "-----BEGIN ENCRYPTED PRIVATE KEY-----"
#define PEM_PKCS8_ENC_KEY_END   "-----END ENCRYPTED PRIVATE KEY-----"

#define PEM_PKCS8_DEC_KEY_BEGIN "-----BEGIN PRIVATE KEY-----"
#define PEM_PKCS8_DEC_KEY_END   "-----END PRIVATE KEY-----"

static gboolean
find_tag (const char *tag,
          const guint8 *data,
          gsize data_len,
          gsize start_at,
          gsize *out_pos)
{
	gsize i, taglen;
	gsize len = data_len - start_at;

	g_return_val_if_fail (out_pos != NULL, FALSE);

	taglen = strlen (tag);
	if (len >= taglen) {
		for (i = 0; i < len - taglen + 1; i++) {
			if (memcmp (data + start_at + i, tag, taglen) == 0) {
				*out_pos = start_at + i;
				return TRUE;
			}
		}
	}
	return FALSE;
}

#define DEK_INFO_TAG "DEK-Info: "
#define PROC_TYPE_TAG "Proc-Type: "

static GByteArray *
parse_old_openssl_key_file (const guint8 *data,
                            gsize data_len,
                            NMCryptoKeyType *out_key_type,
                            char **out_cipher,
                            char **out_iv,
                            GError **error)
{
	GByteArray *bindata = NULL;
	char **lines = NULL;
	char **ln = NULL;
	gsize start = 0, end = 0;
	GString *str = NULL;
	int enc_tags = 0;
	NMCryptoKeyType key_type;
	char *iv = NULL;
	char *cipher = NULL;
	unsigned char *tmp = NULL;
	gsize tmp_len = 0;
	const char *start_tag;
	const char *end_tag;
	guint8 save_end = 0;

	*out_key_type = NM_CRYPTO_KEY_TYPE_UNKNOWN;
	*out_iv = NULL;
	*out_cipher = NULL;

	if (find_tag (PEM_RSA_KEY_BEGIN, data, data_len, 0, &start)) {
		key_type = NM_CRYPTO_KEY_TYPE_RSA;
		start_tag = PEM_RSA_KEY_BEGIN;
		end_tag = PEM_RSA_KEY_END;
	} else if (find_tag (PEM_DSA_KEY_BEGIN, data, data_len, 0, &start)) {
		key_type = NM_CRYPTO_KEY_TYPE_DSA;
		start_tag = PEM_DSA_KEY_BEGIN;
		end_tag = PEM_DSA_KEY_END;
	} else
		goto parse_error;

	start += strlen (start_tag);
	if (!find_tag (end_tag, data, data_len, start, &end)) {
		g_set_error (error, NM_CRYPTO_ERROR,
		             NM_CRYPTO_ERROR_INVALID_DATA,
		             _("PEM key file had no end tag '%s'."),
		             end_tag);
		goto parse_error;
	}

	save_end = data[end];
	((guint8 *)data)[end] = '\0';
	lines = g_strsplit ((const char *) (data + start), "\n", 0);
	((guint8 *)data)[end] = save_end;

	if (!lines || g_strv_length (lines) <= 1) {
		g_set_error (error, NM_CRYPTO_ERROR,
		             NM_CRYPTO_ERROR_INVALID_DATA,
		             _("Doesn't look like a PEM private key file."));
		goto parse_error;
	}

	str = g_string_new_len (NULL, end - start);
	for (ln = lines; *ln; ln++) {
		char *p = *ln;

		/* Chug leading spaces */
		p = g_strstrip (p);
		if (!*p)
			continue;

		if (!strncmp (p, PROC_TYPE_TAG, strlen (PROC_TYPE_TAG))) {
			if (enc_tags++ != 0 || str->len != 0) {
				g_set_error (error, NM_CRYPTO_ERROR,
				             NM_CRYPTO_ERROR_INVALID_DATA,
				             _("Malformed PEM file: Proc-Type was not first tag."));
				goto parse_error;
			}

			p += strlen (PROC_TYPE_TAG);
			if (strcmp (p, "4,ENCRYPTED")) {
				g_set_error (error, NM_CRYPTO_ERROR,
				             NM_CRYPTO_ERROR_INVALID_DATA,
				             _("Malformed PEM file: unknown Proc-Type tag '%s'."),
				             p);
				goto parse_error;
			}
		} else if (!strncmp (p, DEK_INFO_TAG, strlen (DEK_INFO_TAG))) {
			char *comma;

			if (enc_tags++ != 1 || str->len != 0) {
				g_set_error (error, NM_CRYPTO_ERROR,
				             NM_CRYPTO_ERROR_INVALID_DATA,
				             _("Malformed PEM file: DEK-Info was not the second tag."));
				goto parse_error;
			}

			p += strlen (DEK_INFO_TAG);

			/* Grab the IV first */
			comma = strchr (p, ',');
			if (!comma || (*(comma + 1) == '\0')) {
				g_set_error (error, NM_CRYPTO_ERROR,
				             NM_CRYPTO_ERROR_INVALID_DATA,
				             _("Malformed PEM file: no IV found in DEK-Info tag."));
				goto parse_error;
			}
			*comma++ = '\0';
			if (!g_ascii_isxdigit (*comma)) {
				g_set_error (error, NM_CRYPTO_ERROR,
				             NM_CRYPTO_ERROR_INVALID_DATA,
				             _("Malformed PEM file: invalid format of IV in DEK-Info tag."));
				goto parse_error;
			}
			iv = g_strdup (comma);

			/* Get the private key cipher */
			if (!strcasecmp (p, "DES-EDE3-CBC")) {
				cipher = g_strdup (p);
			} else if (!strcasecmp (p, "DES-CBC")) {
				cipher = g_strdup (p);
			} else if (!strcasecmp (p, "AES-128-CBC")) {
				cipher = g_strdup (p);
			} else {
				g_set_error (error, NM_CRYPTO_ERROR,
				             NM_CRYPTO_ERROR_INVALID_DATA,
				             _("Malformed PEM file: unknown private key cipher '%s'."),
				             p);
				goto parse_error;
			}
		} else {
			if (enc_tags == 1) {
				g_set_error (error, NM_CRYPTO_ERROR,
				             NM_CRYPTO_ERROR_INVALID_DATA,
				             "Malformed PEM file: both Proc-Type and DEK-Info tags are required.");
				goto parse_error;
			}
			g_string_append (str, p);
		}
	}

	tmp = g_base64_decode (str->str, &tmp_len);
	if (tmp == NULL || !tmp_len) {
		g_set_error (error, NM_CRYPTO_ERROR,
		             NM_CRYPTO_ERROR_INVALID_DATA,
		             _("Could not decode private key."));
		goto parse_error;
	}
	g_string_free (str, TRUE);

	if (lines)
		g_strfreev (lines);

	bindata = g_byte_array_sized_new (tmp_len);
	g_byte_array_append (bindata, tmp, tmp_len);
	g_free (tmp);

	*out_key_type = key_type;
	*out_iv = iv;
	*out_cipher = cipher;
	return bindata;

parse_error:
	g_free (tmp);
	g_free (cipher);
	g_free (iv);
	if (str)
		g_string_free (str, TRUE);
	if (lines)
		g_strfreev (lines);
	return NULL;
}

static GByteArray *
parse_pkcs8_key_file (const guint8 *data,
                      gsize data_len,
                      gboolean *out_encrypted,
                      GError **error)
{
	GByteArray *key = NULL;
	gsize start = 0, end = 0;
	unsigned char *der = NULL;
	guint8 save_end;
	gsize length = 0;
	const char *start_tag = NULL, *end_tag = NULL;
	gboolean encrypted = FALSE;

	/* Try encrypted first, decrypted next */
	if (find_tag (PEM_PKCS8_ENC_KEY_BEGIN, data, data_len, 0, &start)) {
		start_tag = PEM_PKCS8_ENC_KEY_BEGIN;
		end_tag = PEM_PKCS8_ENC_KEY_END;
		encrypted = TRUE;
	} else if (find_tag (PEM_PKCS8_DEC_KEY_BEGIN, data, data_len, 0, &start)) {
		start_tag = PEM_PKCS8_DEC_KEY_BEGIN;
		end_tag = PEM_PKCS8_DEC_KEY_END;
		encrypted = FALSE;
	} else {
		g_set_error_literal (error, NM_CRYPTO_ERROR,
		                     NM_CRYPTO_ERROR_INVALID_DATA,
		                     _("Failed to find expected PKCS#8 start tag."));
		return NULL;
	}

	start += strlen (start_tag);
	if (!find_tag (end_tag, data, data_len, start, &end)) {
		g_set_error (error, NM_CRYPTO_ERROR,
		             NM_CRYPTO_ERROR_INVALID_DATA,
		             _("Failed to find expected PKCS#8 end tag '%s'."),
		             end_tag);
		return NULL;
	}

	/* g_base64_decode() wants a NULL-terminated string */
	save_end = data[end];
	((guint8 *)data)[end] = '\0';
	der = g_base64_decode ((const char *) (data + start), &length);
	((guint8 *)data)[end] = save_end;

	if (der && length) {
		key = g_byte_array_sized_new (length);
		g_byte_array_append (key, der, length);
		g_assert (key->len == length);
		*out_encrypted = encrypted;
	} else {
		g_set_error_literal (error, NM_CRYPTO_ERROR,
		                     NM_CRYPTO_ERROR_INVALID_DATA,
		                     _("Failed to decode PKCS#8 private key."));
	}

	g_free (der);
	return key;
}

static GByteArray *
file_to_g_byte_array (const char *filename, GError **error)
{
	char *contents;
	GByteArray *array = NULL;
	gsize length = 0;

	if (g_file_get_contents (filename, &contents, &length, error)) {
		array = g_byte_array_sized_new (length);
		g_byte_array_append (array, (guint8 *) contents, length);
		g_assert (array->len == length);
		g_free (contents);
	}
	return array;
}

/*
 * Convert a hex string into bytes.
 */
static char *
convert_iv (const char *src,
            gsize *out_len,
            GError **error)
{
	int num;
	int i;
	char conv[3];
	char *c;

	g_return_val_if_fail (src != NULL, NULL);

	num = strlen (src);
	if (num % 2) {
		g_set_error (error, NM_CRYPTO_ERROR,
		             NM_CRYPTO_ERROR_INVALID_DATA,
		             _("IV must be an even number of bytes in length."));
		return NULL;
	}

	num /= 2;
	c = g_malloc0 (num + 1);

	conv[2] = '\0';
	for (i = 0; i < num; i++) {
		conv[0] = src[(i * 2)];
		conv[1] = src[(i * 2) + 1];
		if (!g_ascii_isxdigit (conv[0]) || !g_ascii_isxdigit (conv[1])) {
			g_set_error (error, NM_CRYPTO_ERROR,
			             NM_CRYPTO_ERROR_INVALID_DATA,
			             _("IV contains non-hexadecimal digits."));
			goto error;
		}

		c[i] = strtol(conv, NULL, 16);
	}
	*out_len = num;
	return c;

error:
	g_free (c);
	return NULL;
}

char *
crypto_make_des_aes_key (const char *cipher,
                         const char *salt,
                         const gsize salt_len,
                         const char *password,
                         gsize *out_len,
                         GError **error)
{
	char *key;
	guint32 digest_len;

	g_return_val_if_fail (cipher != NULL, NULL);
	g_return_val_if_fail (salt != NULL, NULL);
	g_return_val_if_fail (salt_len >= 8, NULL);
	g_return_val_if_fail (password != NULL, NULL);
	g_return_val_if_fail (out_len != NULL, NULL);

	if (!strcmp (cipher, "DES-EDE3-CBC"))
		digest_len = 24;
	else if (!strcmp (cipher, "DES-CBC"))
		digest_len = 8;
	else if (!strcmp (cipher, "AES-128-CBC"))
		digest_len = 16;
	else {
		g_set_error (error, NM_CRYPTO_ERROR,
		             NM_CRYPTO_ERROR_UNKNOWN_CIPHER,
		             _("Private key cipher '%s' was unknown."),
		             cipher);
		return NULL;
	}

	if (password[0] == '\0')
		return NULL;

	key = g_malloc0 (digest_len + 1);

	crypto_md5_hash (salt,
	                 8,
	                 password,
	                 strlen (password),
	                 key,
	                 digest_len);

	*out_len = digest_len;
	return key;
}

static GByteArray *
decrypt_key (const char *cipher,
             int key_type,
             const guint8 *data,
             gsize data_len,
             const char *iv,
             const char *password,
             GError **error)
{
	char *bin_iv = NULL;
	gsize bin_iv_len = 0;
	char *key = NULL;
	gsize key_len = 0;
	char *output = NULL;
	gsize decrypted_len = 0;
	GByteArray *decrypted = NULL;

	g_return_val_if_fail (password != NULL, NULL);

	bin_iv = convert_iv (iv, &bin_iv_len, error);
	if (!bin_iv)
		return NULL;

	/* Convert the password and IV into a DES or AES key */
	key = crypto_make_des_aes_key (cipher, bin_iv, bin_iv_len, password, &key_len, error);
	if (!key || !key_len)
		goto out;

	output = crypto_decrypt (cipher, key_type,
	                         data, data_len,
	                         bin_iv, bin_iv_len,
	                         key, key_len,
	                         &decrypted_len,
	                         error);
	if (output && decrypted_len) {
		decrypted = g_byte_array_sized_new (decrypted_len);
		g_byte_array_append (decrypted, (guint8 *) output, decrypted_len);
	}

out:
	/* Don't leak stale key material */
	if (key)
		memset (key, 0, key_len);
	g_free (output);
	g_free (key);
	g_free (bin_iv);

	return decrypted;
}

GByteArray *
crypto_decrypt_openssl_private_key_data (const guint8 *data,
                                         gsize data_len,
                                         const char *password,
                                         NMCryptoKeyType *out_key_type,
                                         GError **error)
{
	GByteArray *decrypted = NULL;
	NMCryptoKeyType key_type = NM_CRYPTO_KEY_TYPE_UNKNOWN;
	GByteArray *parsed;
	char *iv = NULL;
	char *cipher = NULL;

	g_return_val_if_fail (data != NULL, NULL);
	if (out_key_type)
		g_return_val_if_fail (*out_key_type == NM_CRYPTO_KEY_TYPE_UNKNOWN, NULL);

	if (!crypto_init (error))
		return NULL;

	parsed = parse_old_openssl_key_file (data, data_len, &key_type, &cipher, &iv, NULL);
	/* return the key type even if decryption failed */
	if (out_key_type)
		*out_key_type = key_type;

	if (!parsed) {
		g_set_error (error, NM_CRYPTO_ERROR,
		             NM_CRYPTO_ERROR_INVALID_DATA,
		             _("Unable to determine private key type."));
		return NULL;
	}

	if (password) {
		if (!cipher || !iv) {
			g_set_error (error, NM_CRYPTO_ERROR,
			             NM_CRYPTO_ERROR_INVALID_PASSWORD,
			             _("Password provided, but key was not encrypted."));
		} else {
			decrypted = decrypt_key (cipher,
			                         key_type,
			                         parsed->data,
			                         parsed->len,
			                         iv,
			                         password,
			                         error);
		}
	} else if (!cipher && !iv)
		decrypted = g_byte_array_ref (parsed);

	g_byte_array_unref (parsed);
	g_free (cipher);
	g_free (iv);

	return decrypted;
}

GByteArray *
crypto_decrypt_openssl_private_key (const char *file,
                                    const char *password,
                                    NMCryptoKeyType *out_key_type,
                                    GError **error)
{
	GByteArray *contents;
	GByteArray *key = NULL;

	if (!crypto_init (error))
		return NULL;

	contents = file_to_g_byte_array (file, error);
	if (contents) {
		key = crypto_decrypt_openssl_private_key_data (contents->data, contents->len,
		                                               password, out_key_type, error);
		g_byte_array_free (contents, TRUE);
	}
	return key;
}

static GByteArray *
extract_pem_cert_data (GByteArray *contents, GError **error)
{
	GByteArray *cert = NULL;
	gsize start = 0, end = 0;
	unsigned char *der = NULL;
	guint8 save_end;
	gsize length = 0;

	if (!find_tag (PEM_CERT_BEGIN, contents->data, contents->len, 0, &start)) {
		g_set_error (error, NM_CRYPTO_ERROR,
		             NM_CRYPTO_ERROR_INVALID_DATA,
		             _("PEM certificate had no start tag '%s'."),
		             PEM_CERT_BEGIN);
		goto done;
	}

	start += strlen (PEM_CERT_BEGIN);
	if (!find_tag (PEM_CERT_END, contents->data, contents->len, start, &end)) {
		g_set_error (error, NM_CRYPTO_ERROR,
		             NM_CRYPTO_ERROR_INVALID_DATA,
		             _("PEM certificate had no end tag '%s'."),
		             PEM_CERT_END);
		goto done;
	}

	/* g_base64_decode() wants a NULL-terminated string */
	save_end = contents->data[end];
	contents->data[end] = '\0';
	der = g_base64_decode ((const char *) (contents->data + start), &length);
	contents->data[end] = save_end;

	if (der && length) {
		cert = g_byte_array_sized_new (length);
		g_byte_array_append (cert, der, length);
		g_assert (cert->len == length);
	} else {
		g_set_error (error, NM_CRYPTO_ERROR,
		             NM_CRYPTO_ERROR_INVALID_DATA,
		             _("Failed to decode certificate."));
	}

done:
	g_free (der);
	return cert;
}

GByteArray *
crypto_load_and_verify_certificate (const char *file,
                                    NMCryptoFileFormat *out_file_format,
                                    GError **error)
{
	GByteArray *array, *contents;

	g_return_val_if_fail (file != NULL, NULL);
	g_return_val_if_fail (out_file_format != NULL, NULL);
	g_return_val_if_fail (*out_file_format == NM_CRYPTO_FILE_FORMAT_UNKNOWN, NULL);

	if (!crypto_init (error))
		return NULL;

	contents = file_to_g_byte_array (file, error);
	if (!contents)
		return NULL;

	/* Check for PKCS#12 */
	if (crypto_is_pkcs12_data (contents->data, contents->len, NULL)) {
		*out_file_format = NM_CRYPTO_FILE_FORMAT_PKCS12;
		return contents;
	}

	/* Check for plain DER format */
	if (contents->len > 2 && contents->data[0] == 0x30 && contents->data[1] == 0x82) {
		*out_file_format = crypto_verify_cert (contents->data, contents->len, error);
	} else {
		array = extract_pem_cert_data (contents, error);
		if (!array) {
			g_byte_array_free (contents, TRUE);
			return NULL;
		}

		*out_file_format = crypto_verify_cert (array->data, array->len, error);
		g_byte_array_free (array, TRUE);
	}

	if (*out_file_format != NM_CRYPTO_FILE_FORMAT_X509) {
		g_byte_array_free (contents, TRUE);
		contents = NULL;
	}

	return contents;
}

gboolean
crypto_is_pkcs12_data (const guint8 *data,
                       gsize data_len,
                       GError **error)
{
	GError *local = NULL;
	gboolean success;

	if (!data_len)
		return FALSE;

	g_return_val_if_fail (data != NULL, FALSE);

	if (!crypto_init (error))
		return FALSE;

	success = crypto_verify_pkcs12 (data, data_len, NULL, &local);
	if (success == FALSE) {
		/* If the error was just a decryption error, then it's pkcs#12 */
		if (local) {
			if (g_error_matches (local, NM_CRYPTO_ERROR, NM_CRYPTO_ERROR_DECRYPTION_FAILED)) {
				success = TRUE;
				g_error_free (local);
			} else
				g_propagate_error (error, local);
		}
	}
	return success;
}

gboolean
crypto_is_pkcs12_file (const char *file, GError **error)
{
	GByteArray *contents;
	gboolean success = FALSE;

	g_return_val_if_fail (file != NULL, FALSE);

	if (!crypto_init (error))
		return FALSE;

	contents = file_to_g_byte_array (file, error);
	if (contents) {
		success = crypto_is_pkcs12_data (contents->data, contents->len, error);
		g_byte_array_free (contents, TRUE);
	}
	return success;
}

/* Verifies that a private key can be read, and if a password is given, that
 * the private key can be decrypted with that password.
 */
NMCryptoFileFormat
crypto_verify_private_key_data (const guint8 *data,
                                gsize data_len,
                                const char *password,
                                gboolean *out_is_encrypted,
                                GError **error)
{
	GByteArray *tmp;
	NMCryptoFileFormat format = NM_CRYPTO_FILE_FORMAT_UNKNOWN;
	NMCryptoKeyType ktype = NM_CRYPTO_KEY_TYPE_UNKNOWN;
	gboolean is_encrypted = FALSE;

	g_return_val_if_fail (data != NULL, NM_CRYPTO_FILE_FORMAT_UNKNOWN);
	g_return_val_if_fail (out_is_encrypted == NULL || *out_is_encrypted == FALSE, NM_CRYPTO_FILE_FORMAT_UNKNOWN);

	if (!crypto_init (error))
		return NM_CRYPTO_FILE_FORMAT_UNKNOWN;

	/* Check for PKCS#12 first */
	if (crypto_is_pkcs12_data (data, data_len, NULL)) {
		is_encrypted = TRUE;
		if (!password || crypto_verify_pkcs12 (data, data_len, password, error))
			format = NM_CRYPTO_FILE_FORMAT_PKCS12;
	} else {
		/* Maybe it's PKCS#8 */
		tmp = parse_pkcs8_key_file (data, data_len, &is_encrypted, NULL);
		if (tmp) {
			if (!password || crypto_verify_pkcs8 (tmp->data, tmp->len, is_encrypted, password, error))
				format = NM_CRYPTO_FILE_FORMAT_RAW_KEY;
		} else {
			char *cipher, *iv;

			/* Or it's old-style OpenSSL */
			tmp = parse_old_openssl_key_file (data, data_len, &ktype,
			                                  &cipher, &iv, NULL);
			if (tmp) {
				format = NM_CRYPTO_FILE_FORMAT_RAW_KEY;
				is_encrypted = (cipher && iv);
				g_free (cipher);
				g_free (iv);
			}
		}

		if (tmp) {
			/* Don't leave key data around */
			memset (tmp->data, 0, tmp->len);
			g_byte_array_free (tmp, TRUE);
		}
	}

	if (out_is_encrypted)
		*out_is_encrypted = is_encrypted;
	return format;
}

NMCryptoFileFormat
crypto_verify_private_key (const char *filename,
                           const char *password,
                           gboolean *out_is_encrypted,
                           GError **error)
{
	GByteArray *contents;
	NMCryptoFileFormat format = NM_CRYPTO_FILE_FORMAT_UNKNOWN;

	g_return_val_if_fail (filename != NULL, NM_CRYPTO_FILE_FORMAT_UNKNOWN);

	if (!crypto_init (error))
		return NM_CRYPTO_FILE_FORMAT_UNKNOWN;

	contents = file_to_g_byte_array (filename, error);
	if (contents) {
		format = crypto_verify_private_key_data (contents->data, contents->len, password, out_is_encrypted, error);
		g_byte_array_free (contents, TRUE);
	}
	return format;
}

void
crypto_md5_hash (const char *salt,
                 gssize salt_len,
                 const char *password,
                 gssize password_len,
                 char *buffer,
                 gsize buflen)
{
	GChecksum *ctx;
	gsize digest_len;
	char digest[16];
	gsize bufidx = 0;
	int i;

	nm_assert (g_checksum_type_get_length (G_CHECKSUM_MD5) == sizeof (digest));

	g_return_if_fail (password_len == 0 || password);
	g_return_if_fail (buffer != NULL);
	g_return_if_fail (buflen > 0);
	g_return_if_fail (salt_len == 0 || salt);

	ctx = g_checksum_new (G_CHECKSUM_MD5);

	if (salt_len < 0)
		salt_len = strlen (salt);
	if (password_len < 0)
		password_len = strlen (password);

	for (;;) {
		if (password_len > 0)
			g_checksum_update (ctx, (const guchar *) password, password_len);
		if (salt_len > 0)
			g_checksum_update (ctx, (const guchar *) salt, salt_len);

		digest_len = sizeof (digest);
		g_checksum_get_digest (ctx, (guchar *) digest, &digest_len);
		nm_assert (digest_len == sizeof (digest));

		for (i = 0; i < sizeof (digest); i++) {
			if (bufidx >= buflen)
				goto done;
			buffer[bufidx++] = digest[i];
		}

		g_checksum_reset (ctx);
		g_checksum_update (ctx, (const guchar *) digest, sizeof (digest));
	}

done:
	memset (digest, 0, sizeof (digest));
	g_checksum_free (ctx);
}