/* LibTomCrypt, modular cryptographic library -- Tom St Denis */
/* SPDX-License-Identifier: Unlicense */
#include "tomcrypt_private.h"

/**
  @file pem_ssh.c
  SSH specific functionality to process PEM files, Steffen Jaeckel

  The basic format of the key is described here:
  https://github.com/openssh/openssh-portable/blob/master/PROTOCOL.key
*/

#if defined(LTC_PEM_SSH)

/* Table as of
 * https://www.iana.org/assignments/ssh-parameters/ssh-parameters.xhtml#ssh-parameters-17
 */
const struct blockcipher_info ssh_ciphers[] =
{
   { .name = "none",                          .algo = "",         .keylen = 0,       .mode = cm_none                },
   { .name = "aes128-cbc",                    .algo = "aes",      .keylen = 128 / 8, .mode = cm_cbc                 },
   { .name = "aes128-ctr",                    .algo = "aes",      .keylen = 128 / 8, .mode = cm_ctr                 },
   { .name = "aes192-cbc",                    .algo = "aes",      .keylen = 192 / 8, .mode = cm_cbc                 },
   { .name = "aes192-ctr",                    .algo = "aes",      .keylen = 192 / 8, .mode = cm_ctr                 },
   { .name = "aes256-cbc",                    .algo = "aes",      .keylen = 256 / 8, .mode = cm_cbc                 },
   { .name = "aes256-ctr",                    .algo = "aes",      .keylen = 256 / 8, .mode = cm_ctr                 },
   { .name = "aes128-gcm@openssh.com",        .algo = "aes",      .keylen = 128 / 8, .mode = cm_gcm                 },
   { .name = "aes256-gcm@openssh.com",        .algo = "aes",      .keylen = 256 / 8, .mode = cm_gcm                 },
   { .name = "blowfish128-cbc",               .algo = "blowfish", .keylen = 128 / 8, .mode = cm_cbc                 },
   { .name = "blowfish128-ctr",               .algo = "blowfish", .keylen = 128 / 8, .mode = cm_ctr                 },
   /* The algo name doesn't matter, it's only used in latex-tables */
   { .name = "chacha20-poly1305@openssh.com", .algo = "c20p1305", .keylen = 256 / 8, .mode = cm_stream | cm_openssh },
   { .name = "des-cbc",                       .algo = "des",      .keylen = 64 / 8,  .mode = cm_cbc                 },
   { .name = "3des-cbc",                      .algo = "3des",     .keylen = 192 / 8, .mode = cm_cbc                 },
   { .name = "3des-ctr",                      .algo = "3des",     .keylen = 192 / 8, .mode = cm_ctr                 },
   { .name = "serpent128-cbc",                .algo = "serpent",  .keylen = 128 / 8, .mode = cm_cbc                 },
   { .name = "serpent128-ctr",                .algo = "serpent",  .keylen = 128 / 8, .mode = cm_ctr                 },
   { .name = "serpent192-cbc",                .algo = "serpent",  .keylen = 192 / 8, .mode = cm_cbc                 },
   { .name = "serpent192-ctr",                .algo = "serpent",  .keylen = 192 / 8, .mode = cm_ctr                 },
   { .name = "serpent256-cbc",                .algo = "serpent",  .keylen = 256 / 8, .mode = cm_cbc                 },
   { .name = "serpent256-ctr",                .algo = "serpent",  .keylen = 256 / 8, .mode = cm_ctr                 },
   { .name = "twofish128-cbc",                .algo = "twofish",  .keylen = 128 / 8, .mode = cm_cbc                 },
   { .name = "twofish128-ctr",                .algo = "twofish",  .keylen = 128 / 8, .mode = cm_ctr                 },
   { .name = "twofish192-cbc",                .algo = "twofish",  .keylen = 192 / 8, .mode = cm_cbc                 },
   { .name = "twofish192-ctr",                .algo = "twofish",  .keylen = 192 / 8, .mode = cm_ctr                 },
   { .name = "twofish-cbc",                   .algo = "twofish",  .keylen = 256 / 8, .mode = cm_cbc                 },
   { .name = "twofish256-cbc",                .algo = "twofish",  .keylen = 256 / 8, .mode = cm_cbc                 },
   { .name = "twofish256-ctr",                .algo = "twofish",  .keylen = 256 / 8, .mode = cm_ctr                 },
};
const unsigned long ssh_ciphers_num = LTC_ARRAY_SIZE(ssh_ciphers);

struct kdf_options {
   const char *name;
   const struct blockcipher_info *cipher;
   unsigned char salt[64];
   unsigned long saltlen;
   ulong32 num_rounds;
   struct password pw;
};

#ifdef LTC_MECC
static int s_ssh_find_ecc(const char *pka, const ltc_ecc_curve **curve)
{
   int err;
   const char* prefix = "ecdsa-sha2-";
   unsigned long prefixlen = XSTRLEN(prefix);
   if (strstr(pka, prefix) == NULL) return CRYPT_PK_INVALID_TYPE;
   if ((err = ecc_find_curve(pka + prefixlen, curve)) != CRYPT_OK) return err;
   return CRYPT_OK;
}

static int s_ssh_find_init_ecc(const char *pka, ltc_pka_key *key)
{
   int err;
   const ltc_ecc_curve *cu;
   if ((err = s_ssh_find_ecc(pka, &cu)) != CRYPT_OK) return err;
   return ecc_set_curve(cu, &key->u.ecc);
}

static int s_ssh_decode_ecdsa(const unsigned char *in, unsigned long *inlen, ltc_pka_key *pka_key, enum pem_flags type)
{
   int err;
   unsigned char groupname[64], buf0[512], buf1[512];
   unsigned long groupnamelen = sizeof(groupname), buf0len = sizeof(buf0), buf1len = sizeof(buf1);
   unsigned long remaining, cur_len, keylen;
   const unsigned char *p, *key;

   p = in;
   cur_len = *inlen;
   remaining = *inlen;

   err = ssh_decode_sequence_multi(p, &cur_len,
                                     LTC_SSHDATA_STRING, groupname, &groupnamelen,
                                     LTC_SSHDATA_STRING, buf0, &buf0len,
                                     LTC_SSHDATA_STRING, buf1, &buf1len,
                                     LTC_SSHDATA_EOL,    LTC_NULL);
   if (err == CRYPT_OK) {
      key = buf1;
      keylen = buf1len;
   } else if (err == CRYPT_BUFFER_OVERFLOW && buf0len != sizeof(buf0) && buf1len == sizeof(buf1)) {
      key = buf0;
      keylen = buf0len;
   } else {
      goto cleanup;
   }

   remaining -= cur_len;
   cur_len = remaining;

   err = ecc_set_key(key, keylen, type == pf_public ? PK_PUBLIC : PK_PRIVATE, &pka_key->u.ecc);

cleanup:
   zeromem(groupname, sizeof(groupname));
   zeromem(buf0, sizeof(buf0));
   zeromem(buf1, sizeof(buf1));
   if (err == CRYPT_OK) {
      pka_key->id = LTC_PKA_EC;
      *inlen -= remaining;
   }

   return err;
}
#endif

#ifdef LTC_CURVE25519
static int s_ssh_decode_ed25519(const unsigned char *in, unsigned long *inlen, ltc_pka_key *key, enum pem_flags type)
{
   int err;
   unsigned char pubkey[64], privkey[96];
   unsigned long pubkeylen = sizeof(pubkey), privkeylen = sizeof(privkey);
   unsigned long remaining, cur_len;
   const unsigned char *p;

   p = in;
   cur_len = *inlen;
   remaining = *inlen;

   if ((err = ssh_decode_sequence_multi(p, &cur_len,
                                        LTC_SSHDATA_STRING, pubkey, &pubkeylen,
                                        LTC_SSHDATA_EOL,    LTC_NULL)) != CRYPT_OK) {
      goto cleanup;
   }

   if (type == pf_public) {
      if ((err = ed25519_import_raw(pubkey, pubkeylen, PK_PUBLIC, &key->u.ed25519)) != CRYPT_OK) {
         goto cleanup;
      }
      key->id = LTC_PKA_ED25519;
      goto cleanup;
   }

   p += cur_len;
   remaining -= cur_len;
   cur_len = remaining;

   if ((err = ssh_decode_sequence_multi(p, &cur_len,
                                        LTC_SSHDATA_STRING, privkey, &privkeylen,
                                        LTC_SSHDATA_EOL,    LTC_NULL)) != CRYPT_OK) {
      goto cleanup;
   }
   if ((err = ed25519_import_raw(privkey, privkeylen, PK_PRIVATE, &key->u.ed25519)) != CRYPT_OK) {
      goto cleanup;
   }

   key->id = LTC_PKA_ED25519;

cleanup:
   zeromem(pubkey, sizeof(pubkey));
   zeromem(privkey, sizeof(privkey));
   if (err == CRYPT_OK) {
      remaining -= cur_len;
      *inlen -= remaining;
   }

   return err;
}
#endif

#ifdef LTC_MRSA
static int s_ssh_decode_dsa(const unsigned char *in, unsigned long *inlen, ltc_pka_key *key, enum pem_flags type)
{
   int err, stat;
   unsigned long remaining, cur_len;
   const unsigned char *p;
   if ((err = dsa_int_init(&key->u.dsa)) != CRYPT_OK) {
      return err;
   }

   p = in;
   cur_len = *inlen;
   remaining = *inlen;

   if ((err = ssh_decode_sequence_multi(p, &cur_len,
                                        LTC_SSHDATA_MPINT, key->u.dsa.p,
                                        LTC_SSHDATA_MPINT, key->u.dsa.q,
                                        LTC_SSHDATA_MPINT, key->u.dsa.g,
                                        LTC_SSHDATA_MPINT, key->u.dsa.y,
                                        LTC_SSHDATA_EOL,   LTC_NULL)) != CRYPT_OK) {
      goto cleanup;
   }
   key->u.dsa.qord = ltc_mp_unsigned_bin_size(key->u.dsa.q);
   if ((err = dsa_int_validate_pqg(&key->u.dsa, &stat)) != CRYPT_OK) {
      goto cleanup;
   }
   if (stat == 0) {
      err = CRYPT_INVALID_PACKET;
      goto cleanup;
   }

   if (type == pf_public) {
      key->id = LTC_PKA_DSA;
      key->u.dsa.type = PK_PUBLIC;
      goto cleanup;
   }

   p += cur_len;
   remaining -= cur_len;
   cur_len = remaining;

   if ((err = ssh_decode_sequence_multi(p, &cur_len,
                                        LTC_SSHDATA_MPINT, key->u.dsa.x,
                                        LTC_SSHDATA_EOL,   LTC_NULL)) != CRYPT_OK) {
      goto cleanup;
   }

   key->id = LTC_PKA_DSA;
   key->u.dsa.type = PK_PRIVATE;

cleanup:
   if (err != CRYPT_OK) {
      dsa_free(&key->u.dsa);
   } else {
      remaining -= cur_len;
      *inlen -= remaining;
   }

   return err;

}
#endif

#ifdef LTC_MRSA
static int s_ssh_decode_rsa(const unsigned char *in, unsigned long *inlen, ltc_pka_key *key, enum pem_flags type)
{
   int err;
   void *tmp1, *tmp2;
   unsigned long remaining, cur_len;
   const unsigned char *p;

   if ((err = rsa_init(&key->u.rsa)) != CRYPT_OK) {
      return err;
   }

   p = in;
   cur_len = *inlen;
   remaining = *inlen;

   /* ssh-rsa public and private keys contain `e` and `N` in a different order
    * public contains `e`, then `N`
    * private contains `N`, then `e`
    * change the order later on if we import a public key */
   if ((err = ssh_decode_sequence_multi(p, &cur_len,
                                        LTC_SSHDATA_MPINT, key->u.rsa.N,
                                        LTC_SSHDATA_MPINT, key->u.rsa.e,
                                        LTC_SSHDATA_EOL,   LTC_NULL)) != CRYPT_OK) {
      goto cleanup;
   }

   p += cur_len;
   remaining -= cur_len;
   cur_len = remaining;

   if (type == pf_public) {
      /* c.f. comment above */
      void *exch = key->u.rsa.N;
      key->u.rsa.N = key->u.rsa.e;
      key->u.rsa.e = exch;
      key->id = LTC_PKA_RSA;
      key->u.rsa.type = PK_PUBLIC;
      *inlen -= remaining;
      goto cleanup;
   }

   if ((err = ltc_mp_init_multi(&tmp1, &tmp2, LTC_NULL)) != CRYPT_OK) {
      goto cleanup;
   }

   if ((err = ssh_decode_sequence_multi(p, &cur_len,
                                        LTC_SSHDATA_MPINT, key->u.rsa.d,
                                        LTC_SSHDATA_MPINT, key->u.rsa.qP,
                                        LTC_SSHDATA_MPINT, key->u.rsa.p,
                                        LTC_SSHDATA_MPINT, key->u.rsa.q,
                                        LTC_SSHDATA_EOL,   LTC_NULL)) != CRYPT_OK) {
      goto cleanup_tmps;
   }

   if ((err = ltc_mp_sub_d(key->u.rsa.p, 1, tmp1)) != CRYPT_OK)                   { goto cleanup_tmps; } /* tmp1 = q-1 */
   if ((err = ltc_mp_sub_d(key->u.rsa.q, 1, tmp2)) != CRYPT_OK)                   { goto cleanup_tmps; } /* tmp2 = p-1 */
   if ((err = ltc_mp_mod(key->u.rsa.d, tmp1, key->u.rsa.dP)) != CRYPT_OK)         { goto cleanup_tmps; } /* dP = d mod p-1 */
   if ((err = ltc_mp_mod(key->u.rsa.d, tmp2, key->u.rsa.dQ)) != CRYPT_OK)         { goto cleanup_tmps; } /* dQ = d mod q-1 */

   key->id = LTC_PKA_RSA;
   key->u.rsa.type = PK_PRIVATE;

cleanup_tmps:
   ltc_mp_deinit_multi(tmp2, tmp1, LTC_NULL);
cleanup:
   if (err != CRYPT_OK) {
      rsa_free(&key->u.rsa);
   } else {
      remaining -= cur_len;
      *inlen -= remaining;
   }

   return err;
}
#endif

struct ssh_pka {
   struct str name;
   enum ltc_pka_id id;
   int (*find)(const char*, const ltc_ecc_curve **);
   int (*init)(const char*, ltc_pka_key*);
   int (*decode)(const unsigned char*, unsigned long*, ltc_pka_key*, enum pem_flags);
};

struct ssh_pka ssh_pkas[] = {
#ifdef LTC_CURVE25519
                             { SET_CSTR(.name, "ssh-ed25519"),
                               LTC_PKA_ED25519,
                               NULL,
                               NULL,
                               s_ssh_decode_ed25519 },
#endif
#ifdef LTC_MRSA
                             { SET_CSTR(.name, "ssh-rsa"),
                               LTC_PKA_RSA,
                               NULL,
                               NULL,
                               s_ssh_decode_rsa },
#endif
#ifdef LTC_MDSA
                             { SET_CSTR(.name, "ssh-dss"),
                               LTC_PKA_DSA,
                               NULL,
                               NULL,
                               s_ssh_decode_dsa },
#endif
#ifdef LTC_MECC
                             { { NULL, 0 },
                               LTC_PKA_EC,
                               s_ssh_find_ecc,
                               s_ssh_find_init_ecc,
                               s_ssh_decode_ecdsa },
#endif
};

static int s_decode_key(const unsigned char *in, unsigned long *inlen, ltc_pka_key *key, char **comment, enum pem_flags type)
{
   int err;
   ulong32 check1, check2;
   unsigned char pka[64];
   unsigned long pkalen = sizeof(pka);
   unsigned long remaining, cur_len;
   const unsigned char *p;
   unsigned long n;

   LTC_ARGCHK(in    != NULL);
   LTC_ARGCHK(inlen != NULL);
   LTC_ARGCHK(key   != NULL);

   p = in;
   cur_len = *inlen;
   remaining = *inlen;

   if (type != pf_public) {
      if ((err = ssh_decode_sequence_multi(p, &cur_len,
                                           LTC_SSHDATA_UINT32, &check1,
                                           LTC_SSHDATA_UINT32, &check2,
                                           LTC_SSHDATA_EOL,    LTC_NULL)) != CRYPT_OK) {
         return err;
      }
      if (check1 != check2) {
         return CRYPT_INVALID_PACKET;
      }

      p += cur_len;
      remaining -= cur_len;
      cur_len = remaining;
   }
   if ((err = ssh_decode_sequence_multi(p, &cur_len,
                                        LTC_SSHDATA_STRING, pka, &pkalen,
                                        LTC_SSHDATA_EOL,    LTC_NULL)) != CRYPT_OK) {
      return err;
   }

   p += cur_len;
   remaining -= cur_len;
   cur_len = remaining;

   for (n = 0; n < LTC_ARRAY_SIZE(ssh_pkas); ++n) {
      if (ssh_pkas[n].name.p != NULL) {
         if (pkalen != ssh_pkas[n].name.len
               || XMEMCMP(pka, ssh_pkas[n].name.p, ssh_pkas[n].name.len) != 0) continue;
      } else {
         if ((ssh_pkas[n].init == NULL) ||
               (ssh_pkas[n].init((char*)pka, key) != CRYPT_OK)) continue;
      }
      if ((err = ssh_pkas[n].decode(p, &cur_len, key, type)) != CRYPT_OK) {
         return err;
      }
      break;
   }
   if (n == LTC_ARRAY_SIZE(ssh_pkas)) {
      return CRYPT_PK_INVALID_TYPE;
   }

   p += cur_len;
   remaining -= cur_len;
   cur_len = remaining;

   if (cur_len != 0 && comment) {
      unsigned long commentlen = cur_len;
      char *c = XMALLOC(commentlen);
      if (c == NULL) {
         return CRYPT_MEM;
      }
      if ((err = ssh_decode_sequence_multi(p, &cur_len,
                                           LTC_SSHDATA_STRING, c, &commentlen,
                                           LTC_SSHDATA_EOL,    LTC_NULL)) != CRYPT_OK) {
         return err;
      }
      if (commentlen == 0) {
         XFREE(c);
      } else {
         *comment = c;
      }
   }

   p += cur_len;
   remaining -= cur_len;

   return remaining ? padding_depad(p, &remaining, LTC_PAD_SSH) : CRYPT_OK;
}

static LTC_INLINE void skip_spaces(char **r, unsigned long *l)
{
   while(*l && (**r == ' ' || **r == '\t')) {
      (*r)++;
      (*l)--;
   }
}

static LTC_INLINE void skip_chars(char **r, unsigned long *l)
{
   while(*l && (**r != ' ' && **r != '\t')) {
      (*l)--;
      if (**r == '\n' || **r == '\r') {
         *l = 0;
      } else {
         (*r)++;
      }
   }
}

static LTC_INLINE void skip_to_eol(char **r, unsigned long *l)
{
   while(*l && (**r != '\n' && **r != '\r')) {
      (*l)--;
      (*r)++;
   }
}

static int s_parse_line(char *line, unsigned long *len, ltc_pka_key *key, char **comment)
{
   int err;
   unsigned long n, rlen, olen;
   enum authorized_keys_elements {
      ake_algo_name = 0,
      ake_b64_encoded_key = 1,
      ake_comment = 2
   };
   struct str elements[3] = { 0 };
   char *r = line;
   unsigned char *buf = NULL;

   rlen = *len;
   /* Chop up string into the three authorized_keys_elements */
   for (n = 0; n < LTC_ARRAY_SIZE(elements) && rlen; ++n) {
      skip_spaces(&r, &rlen);
      elements[n].p = r;
      if (n != 2)
         skip_chars(&r, &rlen);
      else
         skip_to_eol(&r, &rlen);
      elements[n].len = r - elements[n].p;
      *r = '\0';
      r++;
   }

   for (n = 0; n < LTC_ARRAY_SIZE(ssh_pkas); ++n) {
      if (ssh_pkas[n].name.p != NULL) {
         if (elements[ake_algo_name].len != ssh_pkas[n].name.len
               || XMEMCMP(elements[ake_algo_name].p, ssh_pkas[n].name.p, ssh_pkas[n].name.len) != 0) continue;
      } else {
         if ((ssh_pkas[n].find == NULL) ||
               (ssh_pkas[n].find(elements[ake_algo_name].p, NULL) != CRYPT_OK)) continue;
      }
      olen = elements[ake_b64_encoded_key].len;
      buf = XMALLOC(olen);
      if (buf == NULL) {
         return CRYPT_MEM;
      }
      if ((err = base64_strict_decode(elements[ake_b64_encoded_key].p, elements[ake_b64_encoded_key].len, buf, &olen)) == CRYPT_OK) {
         err = s_decode_key(buf, &olen, key, comment, pf_public);
         if (err == CRYPT_OK && key->id != ssh_pkas[n].id) {
            err = CRYPT_PK_INVALID_TYPE;
         }
      }
      XFREE(buf);

      if (err == CRYPT_OK) {
         /* Only use the comment that was maybe in the text we just processed, in case when
          * there was no comment inside the SSH key.
          */
         if (*comment == NULL && elements[ake_comment].p) {
            *comment = XMALLOC(elements[ake_comment].len + 1);
            if (*comment == NULL) {
               return CRYPT_MEM;
            }
            XMEMCPY(*comment, elements[ake_comment].p, elements[ake_comment].len);
            (*comment)[elements[ake_comment].len] = '\0';
         }
         *len = r - line;
         return CRYPT_OK;
      }
   }
   return CRYPT_PK_INVALID_TYPE;
}

static int s_read_authorized_keys(const void *buf, unsigned long len, ssh_authorized_key_cb cb, void *ctx)
{
   char *s;
   int err;
   unsigned long clen = len;
   ltc_pka_key *key = XCALLOC(1, sizeof(*key));
   char *comment = NULL;
   void *cpy = XMALLOC(len);
   if (key == NULL || cpy == NULL) {
      if (cpy)
         XFREE(cpy);
      if (key)
         XFREE(key);
      return CRYPT_MEM;
   }
   XMEMCPY(cpy, buf, len);
   s = cpy;
   while (clen && (err = s_parse_line(s, &clen, key, &comment)) == CRYPT_OK) {
      if (cb(key, comment, ctx)) {
         break;
      }
      s += clen;
      len -= clen;
      clen = len;
      key = XCALLOC(1, sizeof(*key));
      if (key == NULL) {
         err = CRYPT_MEM;
         break;
      }
      if (comment) {
         XFREE(comment);
         comment = NULL;
      }
   }
   if (comment)
      XFREE(comment);
   if (cpy)
      XFREE(cpy);
   if (key)
      XFREE(key);
   return err;
}

static int s_decrypt_private_keys(unsigned char *in, unsigned long *inlen,
                                  unsigned char *tag, unsigned long taglen,
                                  struct kdf_options *opts)
{
   int err, cipher;
   unsigned long symkey_len, iv_len;
   unsigned char symkey[MAXBLOCKSIZE], *iv, iv_[8] = { 0 };
   enum cipher_mode mode = opts->cipher->mode & cm_modes;

   LTC_ARGCHK(in    != NULL);
   LTC_ARGCHK(inlen != NULL);
   LTC_ARGCHK(opts  != NULL);

   if (mode != cm_stream) {
      cipher = find_cipher(opts->cipher->algo);
      if (cipher == -1) {
         return CRYPT_INVALID_CIPHER;
      }

      iv = symkey + opts->cipher->keylen;
      iv_len = mode == cm_gcm ? 12 : cipher_descriptor[cipher].block_length;
      symkey_len = opts->cipher->keylen + iv_len;
   } else {
      iv = iv_;
      iv_len = sizeof(iv_);
      symkey_len = 64;
   }

   if (sizeof(symkey) < symkey_len) {
      return CRYPT_OVERFLOW;
   }

   if ((err = bcrypt_pbkdf_openbsd(opts->pw.pw, opts->pw.l, opts->salt, opts->saltlen,
                                   opts->num_rounds, find_hash("sha512"), symkey, &symkey_len)) != CRYPT_OK) {
      return err;
   }
   err = pem_decrypt(in, inlen,
                     symkey, opts->cipher->keylen,
                     iv, iv_len,
                     tag, taglen,
                     opts->cipher, LTC_PAD_SSH);
   zeromem(symkey, sizeof(symkey));

   return err;
}

static int s_decode_header(unsigned char *in, unsigned long *inlen, struct kdf_options *opts)
{
   int err;
   unsigned char ciphername[64], kdfname[64], kdfoptions[128], pubkey1[2048];
   unsigned long ciphernamelen = sizeof(ciphername), kdfnamelen = sizeof(kdfname);
   unsigned long kdfoptionslen = sizeof(kdfoptions), pubkey1len = sizeof(pubkey1);
   ulong32 num_keys;
   unsigned long i;

   void *magic = strstr((const char*)in, "openssh-key-v1");
   unsigned long slen = XSTRLEN("openssh-key-v1");
   unsigned char *start = &in[slen + 1];
   unsigned long len = *inlen - slen - 1;

   if (magic == NULL || magic != in) {
      return CRYPT_INVALID_PACKET;
   }

   if ((err = ssh_decode_sequence_multi(start, &len,
                                        LTC_SSHDATA_STRING, ciphername, &ciphernamelen,
                                        LTC_SSHDATA_STRING, kdfname, &kdfnamelen,
                                        LTC_SSHDATA_STRING, kdfoptions, &kdfoptionslen,
                                        LTC_SSHDATA_UINT32, &num_keys,
                                        LTC_SSHDATA_STRING, pubkey1, &pubkey1len,
                                        LTC_SSHDATA_EOL,    LTC_NULL)) != CRYPT_OK) {
      return err;
   }
   if (num_keys != 1) {
      return CRYPT_INVALID_PACKET;
   }

   *inlen = len + slen + 1;

   for (i = 0; i < ssh_ciphers_num; ++i) {
      if (XSTRCMP((char*)ciphername, ssh_ciphers[i].name) == 0) {
         opts->cipher = &ssh_ciphers[i];
         break;
      }
   }
   if (opts->cipher == NULL) {
      return CRYPT_INVALID_CIPHER;
   }

   if (XSTRCMP((char*)kdfname, "none") == 0) {
      /* NOP */
      opts->name = "none";
   } else if (XSTRCMP((char*)kdfname, "bcrypt") == 0) {
      opts->name = "bcrypt";
      opts->saltlen = sizeof(opts->salt);
      len = kdfoptionslen;
      if ((err = ssh_decode_sequence_multi(kdfoptions, &len,
                                           LTC_SSHDATA_STRING, opts->salt, &opts->saltlen,
                                           LTC_SSHDATA_UINT32, &opts->num_rounds,
                                           LTC_SSHDATA_EOL,    LTC_NULL)) != CRYPT_OK) {
         return err;
      }
      if (len != kdfoptionslen) {
         return CRYPT_INPUT_TOO_LONG;
      }
   } else {
      return CRYPT_INVALID_PACKET;
   }

   return err;
}


static const struct pem_header_id pem_openssh[] = {
   {
     SET_CSTR(.start, "-----BEGIN OPENSSH PRIVATE KEY-----"),
     SET_CSTR(.end, "-----END OPENSSH PRIVATE KEY-----"),
     .has_more_headers = no
   },
   {
     SET_CSTR(.start, "---- BEGIN SSH2 PUBLIC KEY ----"),
     SET_CSTR(.end, "---- END SSH2 PUBLIC KEY ----"),
     .has_more_headers = maybe,
     .flags = pf_public
   },
};
static const unsigned long pem_openssh_num = LTC_ARRAY_SIZE(pem_openssh);

static int s_decode_openssh(struct get_char *g, ltc_pka_key *k, const password_ctx *pw_ctx)
{
   unsigned char *pem = NULL, *p, *privkey = NULL, *tag;
   unsigned long n, w = 0, l, privkey_len, taglen;
   int err;
   struct pem_headers hdr;
   struct kdf_options opts = { 0 };
   XMEMSET(k, 0, sizeof(*k));
   for (n = 0; n < pem_openssh_num; ++n) {
      hdr.id = &pem_openssh[n];
      err = pem_read((void**)&pem, &w, &hdr, g);
      if (err == CRYPT_OK) {
         break;
      } else if (err != CRYPT_UNKNOWN_PEM) {
         goto cleanup;
      }
      hdr.id = NULL;
   }
   /* id not found */
   if (hdr.id == NULL) {
      goto cleanup;
   }
   p = pem;
   l = w;
   if (hdr.id->flags != pf_public) {
      if ((err = s_decode_header(pem, &w, &opts)) != CRYPT_OK) {
         goto cleanup;
      }
      p = pem + w;
      l -= w;
      w = l;

      privkey_len = l;
      privkey = XMALLOC(privkey_len);
      if (privkey == NULL) {
         return CRYPT_MEM;
      }

      if ((err = ssh_decode_sequence_multi(p, &w,
                                           LTC_SSHDATA_STRING, privkey, &privkey_len,
                                           LTC_SSHDATA_EOL,    LTC_NULL)) != CRYPT_OK) {
         goto cleanup;
      }

      if (XSTRCMP(opts.name, "none") != 0) {
         if ((pw_ctx == NULL) || (pw_ctx->callback == NULL)) {
            err = CRYPT_PW_CTX_MISSING;
            goto cleanup;
         }
         if (pw_ctx->callback(&opts.pw.pw, &opts.pw.l, pw_ctx->userdata)) {
            err = CRYPT_ERROR;
            goto cleanup;
         }
         tag = p + w;
         taglen = l - w;
         w = privkey_len;
         if ((err = s_decrypt_private_keys(privkey, &privkey_len,
                                           tag, taglen,
                                           &opts)) != CRYPT_OK) {
            goto cleanup;
         }
         zeromem(opts.pw.pw, opts.pw.l);
      }

      p = privkey;
      w = privkey_len;
   }
   if ((err = s_decode_key(p, &w, k, NULL, hdr.id->flags)) != CRYPT_OK) {
      goto cleanup;
   }

cleanup:
   password_free(&opts.pw, pw_ctx);
   if (privkey) {
      zeromem(privkey, privkey_len);
      XFREE(privkey);
   }
   if (pem) {
      XFREE(pem);
   }
   return err;
}

#ifndef LTC_NO_FILE
int pem_decode_openssh_filehandle(FILE *f, ltc_pka_key *k, const password_ctx *pw_ctx)
{
   LTC_ARGCHK(f != NULL);
   LTC_ARGCHK(k != NULL);
   {
      struct get_char g = pem_get_char_init_filehandle(f);
      return s_decode_openssh(&g, k, pw_ctx);
   }
}

int ssh_read_authorized_keys_filehandle(FILE *f, ssh_authorized_key_cb cb, void *ctx)
{
   size_t tot_data;
   void *buf;
   int err;

   LTC_ARGCHK(f != NULL);
   LTC_ARGCHK(cb != NULL);

   if (fseek(f, 0, SEEK_END) == -1)
      return CRYPT_ERROR;
   tot_data = ftell(f);
   if (fseek(f, 0, SEEK_SET) == -1)
      return CRYPT_ERROR;
   buf = XMALLOC(tot_data);
   if (buf == NULL) {
      return CRYPT_MEM;
   }
   if (fread(buf, 1, tot_data, f) != tot_data) {
      err = CRYPT_ERROR;
   } else {
      err = s_read_authorized_keys(buf, tot_data, cb, ctx);
   }
   XFREE(buf);

   return err;
}
#endif /* LTC_NO_FILE */

int pem_decode_openssh(const void *buf, unsigned long len, ltc_pka_key *k, const password_ctx *pw_ctx)
{
   LTC_ARGCHK(buf != NULL);
   LTC_ARGCHK(len != 0);
   LTC_ARGCHK(k != NULL);
   {
      struct get_char g = pem_get_char_init(buf, len);
      return s_decode_openssh(&g, k, pw_ctx);
   }
}

int ssh_read_authorized_keys(const void *buf, unsigned long len, ssh_authorized_key_cb cb, void *ctx)
{
   LTC_ARGCHK(buf != NULL);
   LTC_ARGCHK(len != 0);
   LTC_ARGCHK(cb != NULL);

   return s_read_authorized_keys(buf, len, cb, ctx);
}
#endif /* defined(LTC_PEM_SSH) */
