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grub-mkpasswd-pbkdf2.c.txt
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grub-mkpasswd-pbkdf2.c.txt
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int
main (int argc, char *argv[])
{
//定义变量可以不管
struct arguments arguments = {
.count = 10000,
.buflen = 64,
.saltlen = 64
};
char *result, *ptr;
gcry_err_code_t gcry_err;
grub_uint8_t *buf, *salt;
char pass1[GRUB_AUTH_MAX_PASSLEN];
char pass2[GRUB_AUTH_MAX_PASSLEN];
//此函数设置变量为程序名称,用处还没搞清楚
grub_util_host_init (&argc, &argv);
//下面是解析参数设置arguments,没设置则使用初始默认值
/* Check for options. */
if (argp_parse (&argp, argc, argv, 0, 0, &arguments) != 0)
{
fprintf (stderr, "%s", _("Error in parsing command line arguments\n"));
exit(1);
}
//分配空间
buf = xmalloc (arguments.buflen);
salt = xmalloc (arguments.saltlen);
//两次读取密码存入对应的pass里,这个获取函数是直接读取键盘按键,不是调用库函数读取的,末尾看下这个函数具体实现
printf ("%s", _("Enter password: "));
if (!grub_password_get (pass1, GRUB_AUTH_MAX_PASSLEN))
{
free (buf);
free (salt);
grub_util_error ("%s", _("failure to read password"));
}
printf ("%s", _("Reenter password: "));
if (!grub_password_get (pass2, GRUB_AUTH_MAX_PASSLEN))
{
free (buf);
free (salt);
grub_util_error ("%s", _("failure to read password"));
}
//确认两次密码一致
if (strcmp (pass1, pass2) != 0)
{
memset (pass1, 0, sizeof (pass1));
memset (pass2, 0, sizeof (pass2));
free (buf);
free (salt);
grub_util_error ("%s", _("passwords don't match"));
}
memset (pass2, 0, sizeof (pass2));
/*
int
grub_get_random (void *out, grub_size_t len)
{
FILE *f;
size_t rd;
f = grub_util_fopen ("/dev/urandom", "rb");
if (!f)
return 1;
rd = fread (out, 1, len, f);
fclose (f);
if (rd != len)
return 1;
return 0;
}
*/
if (grub_get_random (salt, arguments.saltlen))
{
memset (pass1, 0, sizeof (pass1));
free (buf);
free (salt);
grub_util_error ("%s", _("couldn't retrieve random data for salt"));//读取失败这个函数会打印错误并且exit 1直接退出程序
}
//核心加密函数
gcry_err = grub_crypto_pbkdf2 (GRUB_MD_SHA512,
(grub_uint8_t *) pass1, strlen (pass1),
salt, arguments.saltlen,
arguments.count, buf, arguments.buflen);
memset (pass1, 0, sizeof (pass1));
if (gcry_err)
{
memset (buf, 0, arguments.buflen);
free (buf);
memset (salt, 0, arguments.saltlen);
free (salt);
grub_util_error (_("cryptographic error number %d"), gcry_err);
}
result = xmalloc (sizeof ("grub.pbkdf2.sha512.XXXXXXXXXXXXXXXXXXX.S.S")
+ arguments.buflen * 2 + arguments.saltlen * 2);
ptr = result;
//添加前导字符
memcpy (ptr, "grub.pbkdf2.sha512.", sizeof ("grub.pbkdf2.sha512.") - 1);
ptr += sizeof ("grub.pbkdf2.sha512.") - 1;
//写入count
grub_snprintf (ptr, sizeof ("XXXXXXXXXXXXXXXXXXX"), "%d", arguments.count);
ptr += strlen (ptr);
*ptr++ = '.';
hexify (ptr, salt, arguments.saltlen);
ptr += arguments.saltlen * 2;
*ptr++ = '.';
//hexify对位进行某种变换,没看懂源码如下
/*
static void
hexify (char *hex, grub_uint8_t *bin, grub_size_t n)
{
while (n--)
{
if (((*bin & 0xf0) >> 4) < 10)
*hex = ((*bin & 0xf0) >> 4) + '0';
else
*hex = ((*bin & 0xf0) >> 4) + 'A' - 10;
hex++;
if ((*bin & 0xf) < 10)
*hex = (*bin & 0xf) + '0';
else
*hex = (*bin & 0xf) + 'A' - 10;
hex++;
bin++;
}
*hex = 0;
}
*/
hexify (ptr, buf, arguments.buflen);
ptr += arguments.buflen * 2;// 在hexify函数里会倍增,所以ptr需要移动两倍长度
*ptr = '\0';
printf (_("PBKDF2 hash of your password is %s\n"), result);
memset (buf, 0, arguments.buflen);
free (buf);
memset (salt, 0, arguments.saltlen);
free (salt);
return 0;
}
加密函数分析
grub_crypto_pbkdf2 (const struct gcry_md_spec *md,
const grub_uint8_t *P, grub_size_t Plen,
const grub_uint8_t *S, grub_size_t Slen,
unsigned int c,
grub_uint8_t *DK, grub_size_t dkLen)
{
unsigned int hLen = md->mdlen;
grub_uint8_t U[GRUB_CRYPTO_MAX_MDLEN];
grub_uint8_t T[GRUB_CRYPTO_MAX_MDLEN];
unsigned int u;
unsigned int l;
unsigned int r;
unsigned int i;
unsigned int k;
gcry_err_code_t rc;
grub_uint8_t *tmp;
grub_size_t tmplen = Slen + 4;
if (md->mdlen > GRUB_CRYPTO_MAX_MDLEN || md->mdlen == 0)
return GPG_ERR_INV_ARG;
if (c == 0)
return GPG_ERR_INV_ARG;
if (dkLen == 0)
return GPG_ERR_INV_ARG;
if (dkLen > 4294967295U)
return GPG_ERR_INV_ARG;
//以上是参数检查,hLen=64
l = ((dkLen - 1) / hLen) + 1;
r = dkLen - (l - 1) * hLen;
tmp = grub_malloc (tmplen);// tmplen = Slen + 4;
if (tmp == NULL)
return GPG_ERR_OUT_OF_MEMORY;
grub_memcpy (tmp, S, Slen);
for (i = 1; i - 1 < l; i++)
{
grub_memset (T, 0, hLen);
for (u = 0; u < c; u++)
{
if (u == 0)
{
tmp[Slen + 0] = (i & 0xff000000) >> 24;
tmp[Slen + 1] = (i & 0x00ff0000) >> 16;
tmp[Slen + 2] = (i & 0x0000ff00) >> 8;
tmp[Slen + 3] = (i & 0x000000ff) >> 0;
rc = grub_crypto_hmac_buffer (md, P, Plen, tmp, tmplen, U);//利用md接口进行某种位变换,这里没有继续深入
}
else
rc = grub_crypto_hmac_buffer (md, P, Plen, U, hLen, U);
if (rc != GPG_ERR_NO_ERROR)
{
grub_free (tmp);
return rc;
}
for (k = 0; k < hLen; k++)
T[k] ^= U[k];
}
grub_memcpy (DK + (i - 1) * hLen, T, i == l ? r : hLen);
}
grub_free (tmp);
return GPG_ERR_NO_ERROR;
}