git.distorted.org.uk Git - u/mdw/putty/blob - sshpubk.c

   1 /*
   2  * Generic SSH public-key handling operations. In particular,
   3  * reading of SSH public-key files, and also the generic `sign'
   4  * operation for ssh2 (which checks the type of the key and
   5  * dispatches to the appropriate key-type specific function).
   6  */
   7
   8 #include <stdio.h>
   9 #include <stdlib.h>
  10
  11 #include "ssh.h"
  12
  13 #define GET_32BIT(cp) \
  14     (((unsigned long)(unsigned char)(cp)[0] << 24) | \
  15     ((unsigned long)(unsigned char)(cp)[1] << 16) | \
  16     ((unsigned long)(unsigned char)(cp)[2] << 8) | \
  17     ((unsigned long)(unsigned char)(cp)[3]))
  18
  19 #define rsa_signature "SSH PRIVATE KEY FILE FORMAT 1.1\n"
  20
  21 #define BASE64_TOINT(x) ( (x)-'A'<26 ? (x)-'A'+0 :\
  22                           (x)-'a'<26 ? (x)-'a'+26 :\
  23                           (x)-'0'<10 ? (x)-'0'+52 :\
  24                           (x)=='+' ? 62 : \
  25                           (x)=='/' ? 63 : 0 )
  26
  27 static int loadrsakey_main(FILE *fp, struct RSAKey *key,
  28                            char **commentptr, char *passphrase) {
  29     unsigned char buf[16384];
  30     unsigned char keybuf[16];
  31     int len;
  32     int i, j, ciphertype;
  33     int ret = 0;
  34     struct MD5Context md5c;
  35     char *comment;
  36
  37     /* Slurp the whole file (minus the header) into a buffer. */
  38     len = fread(buf, 1, sizeof(buf), fp);
  39     fclose(fp);
  40     if (len < 0 || len == sizeof(buf))
  41         goto end;                      /* file too big or not read */
  42
  43     i = 0;
  44
  45     /*
  46      * A zero byte. (The signature includes a terminating NUL.)
  47      */
  48     if (len-i < 1 || buf[i] != 0)
  49         goto end;
  50     i++;
  51
  52     /* One byte giving encryption type, and one reserved uint32. */
  53     if (len-i < 1)
  54         goto end;
  55     ciphertype = buf[i];
  56     if (ciphertype != 0 && ciphertype != SSH_CIPHER_3DES)
  57         goto end;
  58     i++;
  59     if (len-i < 4)
  60         goto end;                      /* reserved field not present */
  61     if (buf[i] != 0 || buf[i+1] != 0 || buf[i+2] != 0 || buf[i+3] != 0)
  62         goto end;                      /* reserved field nonzero, panic! */
  63     i += 4;
  64
  65     /* Now the serious stuff. An ordinary SSH 1 public key. */
  66     i += makekey(buf+i, key, NULL, 1);
  67     if (len-i < 0)
  68         goto end;                      /* overran */
  69
  70     /* Next, the comment field. */
  71     j = GET_32BIT(buf+i);
  72     i += 4;
  73     if (len-i < j) goto end;
  74     comment = malloc(j+1);
  75     if (comment) {
  76         memcpy(comment, buf+i, j);
  77         comment[j] = '\0';
  78     }
  79     i += j;
  80     if (commentptr)
  81         *commentptr = comment;
  82     if (key)
  83         key->comment = comment;
  84     if (!key) {
  85         return ciphertype != 0;
  86     }
  87
  88     /*
  89      * Decrypt remainder of buffer.
  90      */
  91     if (ciphertype) {
  92         MD5Init(&md5c);
  93         MD5Update(&md5c, passphrase, strlen(passphrase));
  94         MD5Final(keybuf, &md5c);
  95         des3_decrypt_pubkey(keybuf, buf+i, (len-i+7)&~7);
  96         memset(keybuf, 0, sizeof(keybuf));    /* burn the evidence */
  97     }
  98
  99     /*
 100      * We are now in the secret part of the key. The first four
 101      * bytes should be of the form a, b, a, b.
 102      */
 103     if (len-i < 4) goto end;
 104     if (buf[i] != buf[i+2] || buf[i+1] != buf[i+3]) { ret = -1; goto end; }
 105     i += 4;
 106
 107     /*
 108      * After that, we have one further bignum which is our
 109      * decryption modulus, and then we're done.
 110      */
 111     i += makeprivate(buf+i, key);
 112     if (len-i < 0) goto end;
 113
 114     ret = 1;
 115     end:
 116     memset(buf, 0, sizeof(buf));       /* burn the evidence */
 117     return ret;
 118 }
 119
 120 int loadrsakey(char *filename, struct RSAKey *key, char *passphrase) {
 121     FILE *fp;
 122     unsigned char buf[64];
 123
 124     fp = fopen(filename, "rb");
 125     if (!fp)
 126         return 0;                      /* doesn't even exist */
 127
 128     /*
 129      * Read the first line of the file and see if it's a v1 private
 130      * key file.
 131      */
 132     if (fgets(buf, sizeof(buf), fp) &&
 133         !strcmp(buf, rsa_signature)) {
 134         return loadrsakey_main(fp, key, NULL, passphrase);
 135     }
 136
 137     /*
 138      * Otherwise, we have nothing. Return empty-handed.
 139      */
 140     fclose(fp);
 141     return 0;
 142 }
 143
 144 /*
 145  * See whether an RSA key is encrypted. Return its comment field as
 146  * well.
 147  */
 148 int rsakey_encrypted(char *filename, char **comment) {
 149     FILE *fp;
 150     unsigned char buf[64];
 151
 152     fp = fopen(filename, "rb");
 153     if (!fp)
 154         return 0;                      /* doesn't even exist */
 155
 156     /*
 157      * Read the first line of the file and see if it's a v1 private
 158      * key file.
 159      */
 160     if (fgets(buf, sizeof(buf), fp) &&
 161         !strcmp(buf, rsa_signature)) {
 162         return loadrsakey_main(fp, NULL, comment, NULL);
 163     }
 164     return 0;                          /* wasn't the right kind of file */
 165 }