import.c

/*
 * Code for PuTTY to import and export private key files in other
 * SSH clients' formats.
 */

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <ctype.h>

#include "putty.h"
#include "ssh.h"
#include "mpint.h"
#include "misc.h"

static bool openssh_pem_encrypted(BinarySource *src);
static bool openssh_new_encrypted(BinarySource *src);
static ssh2_userkey *openssh_pem_read(
    BinarySource *src, const char *passphrase, const char **errmsg_p);
static ssh2_userkey *openssh_new_read(
    BinarySource *src, const char *passphrase, const char **errmsg_p);
static bool openssh_auto_write(
    const Filename *file, ssh2_userkey *key, const char *passphrase);
static bool openssh_pem_write(
    const Filename *file, ssh2_userkey *key, const char *passphrase);
static bool openssh_new_write(
    const Filename *file, ssh2_userkey *key, const char *passphrase);

static bool sshcom_encrypted(BinarySource *src, char **comment);
static ssh2_userkey *sshcom_read(
    BinarySource *src, const char *passphrase, const char **errmsg_p);
static bool sshcom_write(
    const Filename *file, ssh2_userkey *key, const char *passphrase);

/*
 * Given a key type, determine whether we know how to import it.
 */
bool import_possible(int type)
{
    if (type == SSH_KEYTYPE_OPENSSH_PEM)
        return true;
    if (type == SSH_KEYTYPE_OPENSSH_NEW)
        return true;
    if (type == SSH_KEYTYPE_SSHCOM)
        return true;
    return false;
}

/*
 * Given a key type, determine what native key type
 * (SSH_KEYTYPE_SSH1 or SSH_KEYTYPE_SSH2) it will come out as once
 * we've imported it.
 */
int import_target_type(int type)
{
    /*
     * There are no known foreign SSH-1 key formats.
     */
    return SSH_KEYTYPE_SSH2;
}

static inline char *bsgetline(BinarySource *src)
{
    ptrlen line = get_chomped_line(src);
    if (get_err(src))
        return NULL;
    return mkstr(line);
}

/*
 * Determine whether a foreign key is encrypted.
 */
bool import_encrypted_s(const Filename *filename, BinarySource *src,
                        int type, char **comment)
{
    if (type == SSH_KEYTYPE_OPENSSH_PEM) {
        /* OpenSSH PEM format doesn't contain a key comment at all */
        *comment = dupstr(filename_to_str(filename));
        return openssh_pem_encrypted(src);
    } else if (type == SSH_KEYTYPE_OPENSSH_NEW) {
        /* OpenSSH new format does, but it's inside the encrypted
         * section for some reason */
        *comment = dupstr(filename_to_str(filename));
        return openssh_new_encrypted(src);
    } else if (type == SSH_KEYTYPE_SSHCOM) {
        return sshcom_encrypted(src, comment);
    }
    return false;
}

bool import_encrypted(const Filename *filename, int type, char **comment)
{
    LoadedFile *lf = lf_load_keyfile(filename, NULL);
    if (!lf)
        return false; /* couldn't even open the file */

    bool toret = import_encrypted_s(filename, BinarySource_UPCAST(lf),
                                    type, comment);
    lf_free(lf);
    return toret;
}

/*
 * Import an SSH-1 key.
 */
int import_ssh1_s(BinarySource *src, int type,
                  RSAKey *key, char *passphrase, const char **errmsg_p)
{
    return 0;
}

int import_ssh1(const Filename *filename, int type,
                RSAKey *key, char *passphrase, const char **errmsg_p)
{
    LoadedFile *lf = lf_load_keyfile(filename, errmsg_p);
    if (!lf)
        return false;

    int toret = import_ssh1_s(BinarySource_UPCAST(lf),
                              type, key, passphrase, errmsg_p);
    lf_free(lf);
    return toret;
}

/*
 * Import an SSH-2 key.
 */
ssh2_userkey *import_ssh2_s(BinarySource *src, int type,
                            char *passphrase, const char **errmsg_p)
{
    if (type == SSH_KEYTYPE_OPENSSH_PEM)
        return openssh_pem_read(src, passphrase, errmsg_p);
    else if (type == SSH_KEYTYPE_OPENSSH_NEW)
        return openssh_new_read(src, passphrase, errmsg_p);
    if (type == SSH_KEYTYPE_SSHCOM)
        return sshcom_read(src, passphrase, errmsg_p);
    return NULL;
}

ssh2_userkey *import_ssh2(const Filename *filename, int type,
                          char *passphrase, const char **errmsg_p)
{
    LoadedFile *lf = lf_load_keyfile(filename, errmsg_p);
    if (!lf)
        return false;

    ssh2_userkey *toret = import_ssh2_s(BinarySource_UPCAST(lf),
                                        type, passphrase, errmsg_p);
    lf_free(lf);
    return toret;
}

/*
 * Export an SSH-1 key.
 */
bool export_ssh1(const Filename *filename, int type, RSAKey *key,
                 char *passphrase)
{
    return false;
}

/*
 * Export an SSH-2 key.
 */
bool export_ssh2(const Filename *filename, int type,
                 ssh2_userkey *key, char *passphrase)
{
    if (type == SSH_KEYTYPE_OPENSSH_AUTO)
        return openssh_auto_write(filename, key, passphrase);
    if (type == SSH_KEYTYPE_OPENSSH_NEW)
        return openssh_new_write(filename, key, passphrase);
    if (type == SSH_KEYTYPE_SSHCOM)
        return sshcom_write(filename, key, passphrase);
    return false;
}

/*
 * Strip trailing CRs and LFs at the end of a line of text.
 */
void strip_crlf(char *str)
{
    char *p = str + strlen(str);

    while (p > str && (p[-1] == '\r' || p[-1] == '\n'))
        *--p = '\0';
}

/* ----------------------------------------------------------------------
 * Helper routines. (The base64 ones are defined in sshpubk.c.)
 */

#define isbase64(c) (    ((c) >= 'A' && (c) <= 'Z') || \
                         ((c) >= 'a' && (c) <= 'z') || \
                         ((c) >= '0' && (c) <= '9') || \
                         (c) == '+' || (c) == '/' || (c) == '=' \
                         )

/*
 * Read an ASN.1/BER identifier and length pair.
 *
 * Flags are a combination of the #defines listed below.
 *
 * Returns -1 if unsuccessful; otherwise returns the number of
 * bytes used out of the source data.
 */

/* ASN.1 tag classes. */
#define ASN1_CLASS_UNIVERSAL        (0 << 6)
#define ASN1_CLASS_APPLICATION      (1 << 6)
#define ASN1_CLASS_CONTEXT_SPECIFIC (2 << 6)
#define ASN1_CLASS_PRIVATE          (3 << 6)
#define ASN1_CLASS_MASK             (3 << 6)

/* Primitive versus constructed bit. */
#define ASN1_CONSTRUCTED            (1 << 5)

/*
 * Write an ASN.1/BER identifier and length pair. Returns the
 * number of bytes consumed. Assumes dest contains enough space.
 * Will avoid writing anything if dest is NULL, but still return
 * amount of space required.
 */
static void BinarySink_put_ber_id_len(BinarySink *bs,
                                      int id, int length, int flags)
{
    if (id <= 30) {
        /*
         * Identifier is one byte.
         */
        put_byte(bs, id | flags);
    } else {
        int n;
        /*
         * Identifier is multiple bytes: the first byte is 11111
         * plus the flags, and subsequent bytes encode the value of
         * the identifier, 7 bits at a time, with the top bit of
         * each byte 1 except the last one which is 0.
         */
        put_byte(bs, 0x1F | flags);
        for (n = 1; (id >> (7*n)) > 0; n++)
            continue;                  /* count the bytes */
        while (n--)
            put_byte(bs, (n ? 0x80 : 0) | ((id >> (7*n)) & 0x7F));
    }

    if (length < 128) {
        /*
         * Length is one byte.
         */
        put_byte(bs, length);
    } else {
        int n;
        /*
         * Length is multiple bytes. The first is 0x80 plus the
         * number of subsequent bytes, and the subsequent bytes
         * encode the actual length.
         */
        for (n = 1; (length >> (8*n)) > 0; n++)
            continue;                  /* count the bytes */
        put_byte(bs, 0x80 | n);
        while (n--)
            put_byte(bs, (length >> (8*n)) & 0xFF);
    }
}

#define put_ber_id_len(bs, id, len, flags) \
    BinarySink_put_ber_id_len(BinarySink_UPCAST(bs), id, len, flags)

typedef struct ber_item {
    int id;
    int flags;
    ptrlen data;
} ber_item;

static ber_item BinarySource_get_ber(BinarySource *src)
{
    ber_item toret;
    unsigned char leadbyte, lenbyte;
    size_t length;

    leadbyte = get_byte(src);
    toret.flags = (leadbyte & 0xE0);
    if ((leadbyte & 0x1F) == 0x1F) {
        unsigned char idbyte;

        toret.id = 0;
        do {
            idbyte = get_byte(src);
            toret.id = (toret.id << 7) | (idbyte & 0x7F);
        } while (idbyte & 0x80);
    } else {
        toret.id = leadbyte & 0x1F;
    }

    lenbyte = get_byte(src);
    if (lenbyte & 0x80) {
        int nbytes = lenbyte & 0x7F;
        length = 0;
        while (nbytes-- > 0)
            length = (length << 8) | get_byte(src);
    } else {
        length = lenbyte;
    }

    toret.data = get_data(src, length);
    return toret;
}

#define get_ber(bs) BinarySource_get_ber(BinarySource_UPCAST(bs))

/* ----------------------------------------------------------------------
 * Code to read and write OpenSSH private keys, in the old-style PEM
 * format.
 */

typedef enum {
    OP_DSA, OP_RSA, OP_ECDSA
} openssh_pem_keytype;
typedef enum {
    OP_E_3DES, OP_E_AES
} openssh_pem_enc;

struct openssh_pem_key {
    openssh_pem_keytype keytype;
    bool encrypted;
    openssh_pem_enc encryption;
    char iv[32];
    strbuf *keyblob;
};

void BinarySink_put_mp_ssh2_from_string(BinarySink *bs, ptrlen str)
{
    const unsigned char *bytes = (const unsigned char *)str.ptr;
    size_t nbytes = str.len;
    while (nbytes > 0 && bytes[0] == 0) {
        nbytes--;
        bytes++;
    }
    if (nbytes > 0 && bytes[0] & 0x80) {
        put_uint32(bs, nbytes + 1);
        put_byte(bs, 0);
    } else {
        put_uint32(bs, nbytes);
    }
    put_data(bs, bytes, nbytes);
}
#define put_mp_ssh2_from_string(bs, str) \
    BinarySink_put_mp_ssh2_from_string(BinarySink_UPCAST(bs), str)

static struct openssh_pem_key *load_openssh_pem_key(BinarySource *src,
                                                    const char **errmsg_p)
{
    struct openssh_pem_key *ret;
    char *line = NULL;
    const char *errmsg;
    char *p;
    bool headers_done;
    char base64_bit[4];
    int base64_chars = 0;

    ret = snew(struct openssh_pem_key);
    ret->keyblob = strbuf_new_nm();

    if (!(line = bsgetline(src))) {
        errmsg = "unexpected end of file";
        goto error;
    }
    if (!strstartswith(line, "-----BEGIN ") ||
        !strendswith(line, "PRIVATE KEY-----")) {
        errmsg = "file does not begin with OpenSSH key header";
        goto error;
    }
    /*
     * Parse the BEGIN line. For old-format keys, this tells us the
     * type of the key; for new-format keys, all it tells us is the
     * format, and we'll find out the key type once we parse the
     * base64.
     */
    if (!strcmp(line, "-----BEGIN RSA PRIVATE KEY-----")) {
        ret->keytype = OP_RSA;
    } else if (!strcmp(line, "-----BEGIN DSA PRIVATE KEY-----")) {
        ret->keytype = OP_DSA;
    } else if (!strcmp(line, "-----BEGIN EC PRIVATE KEY-----")) {
        ret->keytype = OP_ECDSA;
    } else if (!strcmp(line, "-----BEGIN OPENSSH PRIVATE KEY-----")) {
        errmsg = "this is a new-style OpenSSH key";
        goto error;
    } else {
        errmsg = "unrecognised key type";
        goto error;
    }
    smemclr(line, strlen(line));
    sfree(line);
    line = NULL;

    ret->encrypted = false;
    memset(ret->iv, 0, sizeof(ret->iv));

    headers_done = false;
    while (1) {
        if (!(line = bsgetline(src))) {
            errmsg = "unexpected end of file";
            goto error;
        }
        if (strstartswith(line, "-----END ") &&
            strendswith(line, "PRIVATE KEY-----")) {
            sfree(line);
            line = NULL;
            break;                     /* done */
        }
        if ((p = strchr(line, ':')) != NULL) {
            if (headers_done) {
                errmsg = "header found in body of key data";
                goto error;
            }
            *p++ = '\0';
            while (*p && isspace((unsigned char)*p)) p++;
            if (!strcmp(line, "Proc-Type")) {
                if (p[0] != '4' || p[1] != ',') {
                    errmsg = "Proc-Type is not 4 (only 4 is supported)";
                    goto error;
                }
                p += 2;
                if (!strcmp(p, "ENCRYPTED"))
                    ret->encrypted = true;
            } else if (!strcmp(line, "DEK-Info")) {
                int i, ivlen;

                if (!strncmp(p, "DES-EDE3-CBC,", 13)) {
                    ret->encryption = OP_E_3DES;
                    ivlen = 8;
                } else if (!strncmp(p, "AES-128-CBC,", 12)) {
                    ret->encryption = OP_E_AES;
                    ivlen = 16;
                } else {
                    errmsg = "unsupported cipher";
                    goto error;
                }
                p = strchr(p, ',') + 1;/* always non-NULL, by above checks */
                for (i = 0; i < ivlen; i++) {
                    unsigned j;
                    if (1 != sscanf(p, "%2x", &j)) {
                        errmsg = "expected more iv data in DEK-Info";
                        goto error;
                    }
                    ret->iv[i] = j;
                    p += 2;
                }
                if (*p) {
                    errmsg = "more iv data than expected in DEK-Info";
                    goto error;
                }
            }
        } else {
            headers_done = true;

            p = line;
            while (isbase64(*p)) {
                base64_bit[base64_chars++] = *p;
                if (base64_chars == 4) {
                    unsigned char out[3];
                    int len;

                    base64_chars = 0;

                    len = base64_decode_atom(base64_bit, out);

                    if (len <= 0) {
                        errmsg = "invalid base64 encoding";
                        goto error;
                    }

                    put_data(ret->keyblob, out, len);

                    smemclr(out, sizeof(out));
                }

                p++;
            }
        }
        smemclr(line, strlen(line));
        sfree(line);
        line = NULL;
    }

    if (!ret->keyblob || ret->keyblob->len == 0) {
        errmsg = "key body not present";
        goto error;
    }

    if (ret->encrypted && ret->keyblob->len % 8 != 0) {
        errmsg = "encrypted key blob is not a multiple of "
            "cipher block size";
        goto error;
    }

    smemclr(base64_bit, sizeof(base64_bit));
    if (errmsg_p) *errmsg_p = NULL;
    return ret;

    error:
    if (line) {
        smemclr(line, strlen(line));
        sfree(line);
        line = NULL;
    }
    smemclr(base64_bit, sizeof(base64_bit));
    if (ret) {
        if (ret->keyblob)
            strbuf_free(ret->keyblob);
        smemclr(ret, sizeof(*ret));
        sfree(ret);
    }
    if (errmsg_p) *errmsg_p = errmsg;
    return NULL;
}

static bool openssh_pem_encrypted(BinarySource *src)
{
    struct openssh_pem_key *key = load_openssh_pem_key(src, NULL);
    bool ret;

    if (!key)
        return false;
    ret = key->encrypted;
    strbuf_free(key->keyblob);
    smemclr(key, sizeof(*key));
    sfree(key);
    return ret;
}

static void openssh_pem_derivekey(
    ptrlen passphrase, const void *iv, uint8_t *keybuf)
{
    /*
     * Derive the encryption key for a PEM key file from the
     * passphrase and iv/salt:
     *
     *  - let block A equal MD5(passphrase || iv)
     *  - let block B equal MD5(A || passphrase || iv)
     *  - block C would be MD5(B || passphrase || iv) and so on
     *  - encryption key is the first N bytes of A || B
     *
     * (Note that only 8 bytes of the iv are used for key
     * derivation, even when the key is encrypted with AES and
     * hence there are 16 bytes available.)
     */
    ssh_hash *h;

    h = ssh_hash_new(&ssh_md5);
    put_datapl(h, passphrase);
    put_data(h, iv, 8);
    ssh_hash_digest(h, keybuf);

    ssh_hash_reset(h);
    put_data(h, keybuf, 16);
    put_datapl(h, passphrase);
    put_data(h, iv, 8);
    ssh_hash_final(h, keybuf + 16);
}

static ssh2_userkey *openssh_pem_read(
    BinarySource *filesrc, const char *passphrase, const char **errmsg_p)
{
    struct openssh_pem_key *key = load_openssh_pem_key(filesrc, errmsg_p);
    ssh2_userkey *retkey;
    const ssh_keyalg *alg;
    BinarySource src[1];
    int i, num_integers;
    ssh2_userkey *retval = NULL;
    const char *errmsg;
    strbuf *blob = strbuf_new_nm();
    int privptr = 0, publen;

    if (!key) {
        strbuf_free(blob);
        return NULL;
    }

    if (key->encrypted) {
        unsigned char keybuf[32];
        openssh_pem_derivekey(ptrlen_from_asciz(passphrase), key->iv, keybuf);

        /*
         * Decrypt the key blob.
         */
        if (key->encryption == OP_E_3DES)
            des3_decrypt_pubkey_ossh(keybuf, key->iv,
                                     key->keyblob->u, key->keyblob->len);
        else {
            ssh_cipher *cipher = ssh_cipher_new(&ssh_aes128_cbc);
            ssh_cipher_setkey(cipher, keybuf);
            ssh_cipher_setiv(cipher, key->iv);
            ssh_cipher_decrypt(cipher, key->keyblob->u, key->keyblob->len);
            ssh_cipher_free(cipher);
        }

        smemclr(keybuf, sizeof(keybuf));
    }

    /*
     * Now we have a decrypted key blob, which contains an ASN.1
     * encoded private key. We must now untangle the ASN.1.
     *
     * We expect the whole key blob to be formatted as a SEQUENCE
     * (0x30 followed by a length code indicating that the rest of
     * the blob is part of the sequence). Within that SEQUENCE we
     * expect to see a bunch of INTEGERs. What those integers mean
     * depends on the key type:
     *
     *  - For RSA, we expect the integers to be 0, n, e, d, p, q,
     *    dmp1, dmq1, iqmp in that order. (The last three are d mod
     *    (p-1), d mod (q-1), inverse of q mod p respectively.)
     *
     *  - For DSA, we expect them to be 0, p, q, g, y, x in that
     *    order.
     *
     *  - In ECDSA the format is totally different: we see the
     *    SEQUENCE, but beneath is an INTEGER 1, OCTET STRING priv
     *    EXPLICIT [0] OID curve, EXPLICIT [1] BIT STRING pubPoint
     */

    BinarySource_BARE_INIT(src, key->keyblob->u, key->keyblob->len);

    {
        /* Expect the SEQUENCE header. Take its absence as a failure to
         * decrypt, if the key was encrypted. */
        ber_item seq = get_ber(src);
        if (get_err(src) || seq.id != 16) {
            errmsg = "ASN.1 decoding failure";
            retval = key->encrypted ? SSH2_WRONG_PASSPHRASE : NULL;
            goto error;
        }

        /* Reinitialise our BinarySource to parse just the inside of that
         * SEQUENCE. */
        BinarySource_BARE_INIT_PL(src, seq.data);
    }

    /* Expect a load of INTEGERs. */
    if (key->keytype == OP_RSA)
        num_integers = 9;
    else if (key->keytype == OP_DSA)
        num_integers = 6;
    else
        num_integers = 0;              /* placate compiler warnings */


    if (key->keytype == OP_ECDSA) {
        /* And now for something completely different */
        ber_item integer, privkey, sub0, sub1, oid, pubkey;
        const ssh_keyalg *alg;
        const struct ec_curve *curve;

        /* Parse the outer layer of things inside the containing SEQUENCE */
        integer = get_ber(src);
        privkey = get_ber(src);
        sub0 = get_ber(src);
        sub1 = get_ber(src);

        /* Now look inside sub0 for the curve OID */
        BinarySource_BARE_INIT_PL(src, sub0.data);
        oid = get_ber(src);

        /* And inside sub1 for the public-key BIT STRING */
        BinarySource_BARE_INIT_PL(src, sub1.data);
        pubkey = get_ber(src);

        if (get_err(src) ||
            integer.id != 2 ||
            integer.data.len != 1 ||
            ((const unsigned char *)integer.data.ptr)[0] != 1 ||
            privkey.id != 4 ||
            sub0.id != 0 ||
            sub1.id != 1 ||
            oid.id != 6 ||
            pubkey.id != 3) {

            errmsg = "ASN.1 decoding failure";
            retval = key->encrypted ? SSH2_WRONG_PASSPHRASE : NULL;
            goto error;
        }

        alg = ec_alg_by_oid(oid.data.len, oid.data.ptr, &curve);
        if (!alg) {
            errmsg = "Unsupported ECDSA curve.";
            retval = NULL;
            goto error;
        }
        if (pubkey.data.len != ((((curve->fieldBits + 7) / 8) * 2) + 2)) {
            errmsg = "ASN.1 decoding failure";
            retval = key->encrypted ? SSH2_WRONG_PASSPHRASE : NULL;
            goto error;
        }
        /* Skip 0x00 before point */
        pubkey.data.ptr = (const char *)pubkey.data.ptr + 1;
        pubkey.data.len -= 1;

        /* Construct the key */
        retkey = snew(ssh2_userkey);

        put_stringz(blob, alg->ssh_id);
        put_stringz(blob, curve->name);
        put_stringpl(blob, pubkey.data);
        publen = blob->len;
        put_mp_ssh2_from_string(blob, privkey.data);

        retkey->key = ssh_key_new_priv(
            alg, make_ptrlen(blob->u, publen),
            make_ptrlen(blob->u + publen, blob->len - publen));

        if (!retkey->key) {
            sfree(retkey);
            errmsg = "unable to create key data structure";
            goto error;
        }

    } else if (key->keytype == OP_RSA || key->keytype == OP_DSA) {

        put_stringz(blob, key->keytype == OP_DSA ? "ssh-dss" : "ssh-rsa");

        ptrlen rsa_modulus = PTRLEN_LITERAL("");

        for (i = 0; i < num_integers; i++) {
            ber_item integer = get_ber(src);

            if (get_err(src) || integer.id != 2) {
                errmsg = "ASN.1 decoding failure";
                retval = key->encrypted ? SSH2_WRONG_PASSPHRASE : NULL;
                goto error;
            }

            if (i == 0) {
                /*
                 * The first integer should be zero always (I think
                 * this is some sort of version indication).
                 */
                if (integer.data.len != 1 ||
                    ((const unsigned char *)integer.data.ptr)[0] != 0) {
                    errmsg = "version number mismatch";
                    goto error;
                }
            } else if (key->keytype == OP_RSA) {
                /*
                 * Integers 1 and 2 go into the public blob but in the
                 * opposite order; integers 3, 4, 5 and 8 go into the
                 * private blob. The other two (6 and 7) are ignored.
                 */
                if (i == 1) {
                    /* Save the details for after we deal with number 2. */
                    rsa_modulus = integer.data;
                } else if (i != 6 && i != 7) {
                    put_mp_ssh2_from_string(blob, integer.data);
                    if (i == 2) {
                        put_mp_ssh2_from_string(blob, rsa_modulus);
                        privptr = blob->len;
                    }
                }
            } else if (key->keytype == OP_DSA) {
                /*
                 * Integers 1-4 go into the public blob; integer 5 goes
                 * into the private blob.
                 */
                put_mp_ssh2_from_string(blob, integer.data);
                if (i == 4)
                    privptr = blob->len;
            }
        }

        /*
         * Now put together the actual key. Simplest way to do this is
         * to assemble our own key blobs and feed them to the createkey
         * functions; this is a bit faffy but it does mean we get all
         * the sanity checks for free.
         */
        assert(privptr > 0);          /* should have bombed by now if not */
        retkey = snew(ssh2_userkey);
        alg = (key->keytype == OP_RSA ? &ssh_rsa : &ssh_dss);
        retkey->key = ssh_key_new_priv(
            alg, make_ptrlen(blob->u, privptr),
            make_ptrlen(blob->u+privptr, blob->len-privptr));

        if (!retkey->key) {
            sfree(retkey);
            errmsg = "unable to create key data structure";
            goto error;
        }

    } else {
        unreachable("Bad key type from load_openssh_pem_key");
        errmsg = "Bad key type from load_openssh_pem_key";
        goto error;
    }

    /*
     * The old key format doesn't include a comment in the private
     * key file.
     */
    retkey->comment = dupstr("imported-openssh-key");

    errmsg = NULL;                     /* no error */
    retval = retkey;

    error:
    strbuf_free(blob);
    strbuf_free(key->keyblob);
    smemclr(key, sizeof(*key));
    sfree(key);
    if (errmsg_p) *errmsg_p = errmsg;
    return retval;
}

static bool openssh_pem_write(
    const Filename *filename, ssh2_userkey *key, const char *passphrase)
{
    strbuf *pubblob, *privblob, *outblob;
    unsigned char *spareblob;
    int sparelen = 0;
    ptrlen numbers[9];
    int nnumbers, i;
    const char *header, *footer;
    char zero[1];
    unsigned char iv[8];
    bool ret = false;
    FILE *fp;
    BinarySource src[1];

    /*
     * Fetch the key blobs.
     */
    pubblob = strbuf_new();
    ssh_key_public_blob(key->key, BinarySink_UPCAST(pubblob));
    privblob = strbuf_new_nm();
    ssh_key_private_blob(key->key, BinarySink_UPCAST(privblob));
    spareblob = NULL;

    outblob = strbuf_new_nm();

    /*
     * Encode the OpenSSH key blob, and also decide on the header
     * line.
     */
    if (ssh_key_alg(key->key) == &ssh_rsa ||
        ssh_key_alg(key->key) == &ssh_dss) {
        strbuf *seq;

        /*
         * The RSA and DSS handlers share some code because the two
         * key types have very similar ASN.1 representations, as a
         * plain SEQUENCE of big integers. So we set up a list of
         * bignums per key type and then construct the actual blob in
         * common code after that.
         */
        if (ssh_key_alg(key->key) == &ssh_rsa) {
            ptrlen n, e, d, p, q, iqmp, dmp1, dmq1;
            mp_int *bd, *bp, *bq, *bdmp1, *bdmq1;

            /*
             * These blobs were generated from inside PuTTY, so we needn't
             * treat them as untrusted.
             */
            BinarySource_BARE_INIT(src, pubblob->u, pubblob->len);
            get_string(src);           /* skip algorithm name */
            e = get_string(src);
            n = get_string(src);
            BinarySource_BARE_INIT(src, privblob->u, privblob->len);
            d = get_string(src);
            p = get_string(src);
            q = get_string(src);
            iqmp = get_string(src);

            assert(!get_err(src));     /* can't go wrong */

            /* We also need d mod (p-1) and d mod (q-1). */
            bd = mp_from_bytes_be(d);
            bp = mp_from_bytes_be(p);
            bq = mp_from_bytes_be(q);
            mp_sub_integer_into(bp, bp, 1);
            mp_sub_integer_into(bq, bq, 1);
            bdmp1 = mp_mod(bd, bp);
            bdmq1 = mp_mod(bd, bq);
            mp_free(bd);
            mp_free(bp);
            mp_free(bq);

            dmp1.len = (mp_get_nbits(bdmp1)+8)/8;
            dmq1.len = (mp_get_nbits(bdmq1)+8)/8;
            sparelen = dmp1.len + dmq1.len;
            spareblob = snewn(sparelen, unsigned char);
            dmp1.ptr = spareblob;
            dmq1.ptr = spareblob + dmp1.len;
            for (i = 0; i < dmp1.len; i++)
                spareblob[i] = mp_get_byte(bdmp1, dmp1.len-1 - i);
            for (i = 0; i < dmq1.len; i++)
                spareblob[i+dmp1.len] = mp_get_byte(bdmq1, dmq1.len-1 - i);
            mp_free(bdmp1);
            mp_free(bdmq1);

            numbers[0] = make_ptrlen(zero, 1); zero[0] = '\0';
            numbers[1] = n;
            numbers[2] = e;
            numbers[3] = d;
            numbers[4] = p;
            numbers[5] = q;
            numbers[6] = dmp1;
            numbers[7] = dmq1;
            numbers[8] = iqmp;

            nnumbers = 9;
            header = "-----BEGIN RSA PRIVATE KEY-----\n";
            footer = "-----END RSA PRIVATE KEY-----\n";
        } else {                       /* ssh-dss */
            ptrlen p, q, g, y, x;

            /*
             * These blobs were generated from inside PuTTY, so we needn't
             * treat them as untrusted.
             */
            BinarySource_BARE_INIT(src, pubblob->u, pubblob->len);
            get_string(src);           /* skip algorithm name */
            p = get_string(src);
            q = get_string(src);
            g = get_string(src);
            y = get_string(src);
            BinarySource_BARE_INIT(src, privblob->u, privblob->len);
            x = get_string(src);

            assert(!get_err(src));     /* can't go wrong */

            numbers[0].ptr = zero; numbers[0].len = 1; zero[0] = '\0';
            numbers[1] = p;
            numbers[2] = q;
            numbers[3] = g;
            numbers[4] = y;
            numbers[5] = x;

            nnumbers = 6;
            header = "-----BEGIN DSA PRIVATE KEY-----\n";
            footer = "-----END DSA PRIVATE KEY-----\n";
        }

        seq = strbuf_new_nm();
        for (i = 0; i < nnumbers; i++) {
            put_ber_id_len(seq, 2, numbers[i].len, 0);
            put_datapl(seq, numbers[i]);
        }
        put_ber_id_len(outblob, 16, seq->len, ASN1_CONSTRUCTED);
        put_data(outblob, seq->s, seq->len);
        strbuf_free(seq);
    } else if (ssh_key_alg(key->key) == &ssh_ecdsa_nistp256 ||
               ssh_key_alg(key->key) == &ssh_ecdsa_nistp384 ||
               ssh_key_alg(key->key) == &ssh_ecdsa_nistp521) {
        const unsigned char *oid;
        struct ecdsa_key *ec = container_of(key->key, struct ecdsa_key, sshk);
        int oidlen;
        int pointlen;
        strbuf *seq, *sub;

        /*
         * Structure of asn1:
         * SEQUENCE
         *   INTEGER 1
         *   OCTET STRING (private key)
         *   [0]
         *     OID (curve)
         *   [1]
         *     BIT STRING (0x00 public key point)
         */
        oid = ec_alg_oid(ssh_key_alg(key->key), &oidlen);
        pointlen = (ec->curve->fieldBits + 7) / 8 * 2;

        seq = strbuf_new_nm();

        /* INTEGER 1 */
        put_ber_id_len(seq, 2, 1, 0);
        put_byte(seq, 1);

        /* OCTET STRING private key */
        put_ber_id_len(seq, 4, privblob->len - 4, 0);
        put_data(seq, privblob->s + 4, privblob->len - 4);

        /* Subsidiary OID */
        sub = strbuf_new();
        put_ber_id_len(sub, 6, oidlen, 0);
        put_data(sub, oid, oidlen);

        /* Append the OID to the sequence */
        put_ber_id_len(seq, 0, sub->len,
                       ASN1_CLASS_CONTEXT_SPECIFIC | ASN1_CONSTRUCTED);
        put_data(seq, sub->s, sub->len);
        strbuf_free(sub);

        /* Subsidiary BIT STRING */
        sub = strbuf_new();
        put_ber_id_len(sub, 3, 2 + pointlen, 0);
        put_byte(sub, 0);
        put_data(sub, pubblob->s+39, 1 + pointlen);

        /* Append the BIT STRING to the sequence */
        put_ber_id_len(seq, 1, sub->len,