putty/pageant.c

/*
 * pageant.c: cross-platform code to implement Pageant.
 */

#include <stddef.h>
#include <stdlib.h>
#include <assert.h>

#include "putty.h"
#include "ssh.h"
#include "pageant.h"

/*
 * We need this to link with the RSA code, because rsaencrypt()
 * pads its data with random bytes. Since we only use rsadecrypt()
 * and the signing functions, which are deterministic, this should
 * never be called.
 *
 * If it _is_ called, there is a _serious_ problem, because it
 * won't generate true random numbers. So we must scream, panic,
 * and exit immediately if that should happen.
 */
int random_byte(void)
{
    modalfatalbox("Internal error: attempt to use random numbers in Pageant");
    exit(0);
    return 0;                 /* unreachable, but placate optimiser */
}

/*
 * rsakeys stores SSH-1 RSA keys. ssh2keys stores all SSH-2 keys.
 */
static tree234 *rsakeys, *ssh2keys;

/*
 * Blob structure for passing to the asymmetric SSH-2 key compare
 * function, prototyped here.
 */
struct blob {
    const unsigned char *blob;
    int len;
};
static int cmpkeys_ssh2_asymm(void *av, void *bv);

/*
 * Key comparison function for the 2-3-4 tree of RSA keys.
 */
static int cmpkeys_rsa(void *av, void *bv)
{
    struct RSAKey *a = (struct RSAKey *) av;
    struct RSAKey *b = (struct RSAKey *) bv;
    Bignum am, bm;
    int alen, blen;

    am = a->modulus;
    bm = b->modulus;
    /*
     * Compare by length of moduli.
     */
    alen = bignum_bitcount(am);
    blen = bignum_bitcount(bm);
    if (alen > blen)
	return +1;
    else if (alen < blen)
	return -1;
    /*
     * Now compare by moduli themselves.
     */
    alen = (alen + 7) / 8;	       /* byte count */
    while (alen-- > 0) {
	int abyte, bbyte;
	abyte = bignum_byte(am, alen);
	bbyte = bignum_byte(bm, alen);
	if (abyte > bbyte)
	    return +1;
	else if (abyte < bbyte)
	    return -1;
    }
    /*
     * Give up.
     */
    return 0;
}

/*
 * Key comparison function for the 2-3-4 tree of SSH-2 keys.
 */
static int cmpkeys_ssh2(void *av, void *bv)
{
    struct ssh2_userkey *a = (struct ssh2_userkey *) av;
    struct ssh2_userkey *b = (struct ssh2_userkey *) bv;
    int i;
    int alen, blen;
    unsigned char *ablob, *bblob;
    int c;

    /*
     * Compare purely by public blob.
     */
    ablob = a->alg->public_blob(a->data, &alen);
    bblob = b->alg->public_blob(b->data, &blen);

    c = 0;
    for (i = 0; i < alen && i < blen; i++) {
	if (ablob[i] < bblob[i]) {
	    c = -1;
	    break;
	} else if (ablob[i] > bblob[i]) {
	    c = +1;
	    break;
	}
    }
    if (c == 0 && i < alen)
	c = +1;			       /* a is longer */
    if (c == 0 && i < blen)
	c = -1;			       /* a is longer */

    sfree(ablob);
    sfree(bblob);

    return c;
}

/*
 * Key comparison function for looking up a blob in the 2-3-4 tree
 * of SSH-2 keys.
 */
static int cmpkeys_ssh2_asymm(void *av, void *bv)
{
    struct blob *a = (struct blob *) av;
    struct ssh2_userkey *b = (struct ssh2_userkey *) bv;
    int i;
    int alen, blen;
    const unsigned char *ablob;
    unsigned char *bblob;
    int c;

    /*
     * Compare purely by public blob.
     */
    ablob = a->blob;
    alen = a->len;
    bblob = b->alg->public_blob(b->data, &blen);

    c = 0;
    for (i = 0; i < alen && i < blen; i++) {
	if (ablob[i] < bblob[i]) {
	    c = -1;
	    break;
	} else if (ablob[i] > bblob[i]) {
	    c = +1;
	    break;
	}
    }
    if (c == 0 && i < alen)
	c = +1;			       /* a is longer */
    if (c == 0 && i < blen)
	c = -1;			       /* a is longer */

    sfree(bblob);

    return c;
}

/*
 * Create an SSH-1 key list in a malloc'ed buffer; return its
 * length.
 */
void *pageant_make_keylist1(int *length)
{
    int i, nkeys, len;
    struct RSAKey *key;
    unsigned char *blob, *p, *ret;
    int bloblen;

    /*
     * Count up the number and length of keys we hold.
     */
    len = 4;
    nkeys = 0;
    for (i = 0; NULL != (key = index234(rsakeys, i)); i++) {
	nkeys++;
	blob = rsa_public_blob(key, &bloblen);
	len += bloblen;
	sfree(blob);
	len += 4 + strlen(key->comment);
    }

    /* Allocate the buffer. */
    p = ret = snewn(len, unsigned char);
    if (length) *length = len;

    PUT_32BIT(p, nkeys);
    p += 4;
    for (i = 0; NULL != (key = index234(rsakeys, i)); i++) {
	blob = rsa_public_blob(key, &bloblen);
	memcpy(p, blob, bloblen);
	p += bloblen;
	sfree(blob);
	PUT_32BIT(p, strlen(key->comment));
	memcpy(p + 4, key->comment, strlen(key->comment));
	p += 4 + strlen(key->comment);
    }

    assert(p - ret == len);
    return ret;
}

/*
 * Create an SSH-2 key list in a malloc'ed buffer; return its
 * length.
 */
void *pageant_make_keylist2(int *length)
{
    struct ssh2_userkey *key;
    int i, len, nkeys;
    unsigned char *blob, *p, *ret;
    int bloblen;

    /*
     * Count up the number and length of keys we hold.
     */
    len = 4;
    nkeys = 0;
    for (i = 0; NULL != (key = index234(ssh2keys, i)); i++) {
	nkeys++;
	len += 4;	       /* length field */
	blob = key->alg->public_blob(key->data, &bloblen);
	len += bloblen;
	sfree(blob);
	len += 4 + strlen(key->comment);
    }

    /* Allocate the buffer. */
    p = ret = snewn(len, unsigned char);
    if (length) *length = len;

    /*
     * Packet header is the obvious five bytes, plus four
     * bytes for the key count.
     */
    PUT_32BIT(p, nkeys);
    p += 4;
    for (i = 0; NULL != (key = index234(ssh2keys, i)); i++) {
	blob = key->alg->public_blob(key->data, &bloblen);
	PUT_32BIT(p, bloblen);
	p += 4;
	memcpy(p, blob, bloblen);
	p += bloblen;
	sfree(blob);
	PUT_32BIT(p, strlen(key->comment));
	memcpy(p + 4, key->comment, strlen(key->comment));
	p += 4 + strlen(key->comment);
    }

    assert(p - ret == len);
    return ret;
}

void *pageant_handle_msg(const void *msg, int msglen, int *outlen)
{
    const unsigned char *p = msg;
    const unsigned char *msgend;
    unsigned char *ret = snewn(AGENT_MAX_MSGLEN, unsigned char);
    int type;

    msgend = p + msglen;

    /*
     * Get the message type.
     */
    if (msgend < p+1)
	goto failure;
    type = *p++;

    switch (type) {
      case SSH1_AGENTC_REQUEST_RSA_IDENTITIES:
	/*
	 * Reply with SSH1_AGENT_RSA_IDENTITIES_ANSWER.
	 */
	{
	    int len;
	    void *keylist;

	    ret[4] = SSH1_AGENT_RSA_IDENTITIES_ANSWER;
	    keylist = pageant_make_keylist1(&len);
	    if (len + 5 > AGENT_MAX_MSGLEN) {
		sfree(keylist);
		goto failure;
	    }
	    PUT_32BIT(ret, len + 1);
	    memcpy(ret + 5, keylist, len);
	    sfree(keylist);
	}
	break;
      case SSH2_AGENTC_REQUEST_IDENTITIES:
	/*
	 * Reply with SSH2_AGENT_IDENTITIES_ANSWER.
	 */
	{
	    int len;
	    void *keylist;

	    ret[4] = SSH2_AGENT_IDENTITIES_ANSWER;
	    keylist = pageant_make_keylist2(&len);
	    if (len + 5 > AGENT_MAX_MSGLEN) {
		sfree(keylist);
		goto failure;
	    }
	    PUT_32BIT(ret, len + 1);
	    memcpy(ret + 5, keylist, len);
	    sfree(keylist);
	}
	break;
      case SSH1_AGENTC_RSA_CHALLENGE:
	/*
	 * Reply with either SSH1_AGENT_RSA_RESPONSE or
	 * SSH_AGENT_FAILURE, depending on whether we have that key
	 * or not.
	 */
	{
	    struct RSAKey reqkey, *key;
	    Bignum challenge, response;
	    unsigned char response_source[48], response_md5[16];
	    struct MD5Context md5c;
	    int i, len;

	    p += 4;
	    i = ssh1_read_bignum(p, msgend - p, &reqkey.exponent);
	    if (i < 0)
		goto failure;
	    p += i;
	    i = ssh1_read_bignum(p, msgend - p, &reqkey.modulus);
	    if (i < 0) {
                freebn(reqkey.exponent);
		goto failure;
            }
	    p += i;
	    i = ssh1_read_bignum(p, msgend - p, &challenge);
	    if (i < 0) {
                freebn(reqkey.exponent);
                freebn(reqkey.modulus);
		goto failure;
            }
	    p += i;
	    if (msgend < p+16) {
		freebn(reqkey.exponent);
		freebn(reqkey.modulus);
		freebn(challenge);
		goto failure;
	    }
	    memcpy(response_source + 32, p, 16);
	    p += 16;
	    if (msgend < p+4 ||
		GET_32BIT(p) != 1 ||
		(key = find234(rsakeys, &reqkey, NULL)) == NULL) {
		freebn(reqkey.exponent);
		freebn(reqkey.modulus);
		freebn(challenge);
		goto failure;
	    }
	    response = rsadecrypt(challenge, key);
	    for (i = 0; i < 32; i++)
		response_source[i] = bignum_byte(response, 31 - i);

	    MD5Init(&md5c);
	    MD5Update(&md5c, response_source, 48);
	    MD5Final(response_md5, &md5c);
	    smemclr(response_source, 48);	/* burn the evidence */
	    freebn(response);	       /* and that evidence */
	    freebn(challenge);	       /* yes, and that evidence */
	    freebn(reqkey.exponent);   /* and free some memory ... */
	    freebn(reqkey.modulus);    /* ... while we're at it. */

	    /*
	     * Packet is the obvious five byte header, plus sixteen
	     * bytes of MD5.
	     */
	    len = 5 + 16;
	    PUT_32BIT(ret, len - 4);
	    ret[4] = SSH1_AGENT_RSA_RESPONSE;
	    memcpy(ret + 5, response_md5, 16);
	}
	break;
      case SSH2_AGENTC_SIGN_REQUEST:
	/*
	 * Reply with either SSH2_AGENT_SIGN_RESPONSE or
	 * SSH_AGENT_FAILURE, depending on whether we have that key
	 * or not.
	 */
	{
	    struct ssh2_userkey *key;
	    struct blob b;
	    const unsigned char *data;
            unsigned char *signature;
	    int datalen, siglen, len;

	    if (msgend < p+4)
		goto failure;
	    b.len = toint(GET_32BIT(p));
            if (b.len < 0 || b.len > msgend - (p+4))
                goto failure;
	    p += 4;
	    b.blob = p;
	    p += b.len;
	    if (msgend < p+4)
		goto failure;
	    datalen = toint(GET_32BIT(p));
	    p += 4;
	    if (datalen < 0 || datalen > msgend - p)
		goto failure;
	    data = p;
	    key = find234(ssh2keys, &b, cmpkeys_ssh2_asymm);
	    if (!key)
		goto failure;
	    signature = key->alg->sign(key->data, (const char *)data,
                                       datalen, &siglen);
	    len = 5 + 4 + siglen;
	    PUT_32BIT(ret, len - 4);
	    ret[4] = SSH2_AGENT_SIGN_RESPONSE;
	    PUT_32BIT(ret + 5, siglen);
	    memcpy(ret + 5 + 4, signature, siglen);
	    sfree(signature);
	}
	break;
      case SSH1_AGENTC_ADD_RSA_IDENTITY:
	/*
	 * Add to the list and return SSH_AGENT_SUCCESS, or
	 * SSH_AGENT_FAILURE if the key was malformed.
	 */
	{
	    struct RSAKey *key;
	    char *comment;
            int n, commentlen;

	    key = snew(struct RSAKey);
	    memset(key, 0, sizeof(struct RSAKey));

	    n = makekey(p, msgend - p, key, NULL, 1);
	    if (n < 0) {
		freersakey(key);
		sfree(key);
		goto failure;
	    }
	    p += n;

	    n = makeprivate(p, msgend - p, key);
	    if (n < 0) {
		freersakey(key);
		sfree(key);
		goto failure;
	    }
	    p += n;

	    n = ssh1_read_bignum(p, msgend - p, &key->iqmp);  /* p^-1 mod q */
	    if (n < 0) {
		freersakey(key);
		sfree(key);
		goto failure;
	    }
	    p += n;

	    n = ssh1_read_bignum(p, msgend - p, &key->p);  /* p */
	    if (n < 0) {
		freersakey(key);
		sfree(key);
		goto failure;
	    }
	    p += n;

	    n = ssh1_read_bignum(p, msgend - p, &key->q);  /* q */
	    if (n < 0) {
		freersakey(key);
		sfree(key);
		goto failure;
	    }
	    p += n;

	    if (msgend < p+4) {
		freersakey(key);
		sfree(key);
		goto failure;
	    }
            commentlen = toint(GET_32BIT(p));

	    if (commentlen < 0 || commentlen > msgend - p) {
		freersakey(key);
		sfree(key);
		goto failure;
	    }

	    comment = snewn(commentlen+1, char);
	    if (comment) {
		memcpy(comment, p + 4, commentlen);
                comment[commentlen] = '\0';
		key->comment = comment;
	    }
	    PUT_32BIT(ret, 1);
	    ret[4] = SSH_AGENT_FAILURE;
	    if (add234(rsakeys, key) == key) {
		keylist_update();
		ret[4] = SSH_AGENT_SUCCESS;
	    } else {
		freersakey(key);
		sfree(key);
	    }
	}
	break;
      case SSH2_AGENTC_ADD_IDENTITY:
	/*
	 * Add to the list and return SSH_AGENT_SUCCESS, or
	 * SSH_AGENT_FAILURE if the key was malformed.
	 */
	{
	    struct ssh2_userkey *key;
	    char *comment;
            const char *alg;
	    int alglen, commlen;
	    int bloblen;


	    if (msgend < p+4)
		goto failure;
	    alglen = toint(GET_32BIT(p));
	    p += 4;
	    if (alglen < 0 || alglen > msgend - p)
		goto failure;
	    alg = (const char *)p;
	    p += alglen;

	    key = snew(struct ssh2_userkey);
	    /* Add further algorithm names here. */
	    if (alglen == 7 && !memcmp(alg, "ssh-rsa", 7))
		key->alg = &ssh_rsa;
	    else if (alglen == 7 && !memcmp(alg, "ssh-dss", 7))
		key->alg = &ssh_dss;
            else if (alglen == 19 && memcmp(alg, "ecdsa-sha2-nistp256", 19))
                key->alg = &ssh_ecdsa_nistp256;
            else if (alglen == 19 && memcmp(alg, "ecdsa-sha2-nistp384", 19))
                key->alg = &ssh_ecdsa_nistp384;
            else if (alglen == 19 && memcmp(alg, "ecdsa-sha2-nistp521", 19))
                key->alg = &ssh_ecdsa_nistp521;
	    else {
		sfree(key);
		goto failure;
	    }

	    bloblen = msgend - p;
	    key->data = key->alg->openssh_createkey(&p, &bloblen);
	    if (!key->data) {
		sfree(key);
		goto failure;
	    }

	    /*
	     * p has been advanced by openssh_createkey, but
	     * certainly not _beyond_ the end of the buffer.
	     */
	    assert(p <= msgend);

	    if (msgend < p+4) {
		key->alg->freekey(key->data);
		sfree(key);
		goto failure;
	    }
	    commlen = toint(GET_32BIT(p));
	    p += 4;

	    if (commlen < 0 || commlen > msgend - p) {
		key->alg->freekey(key->data);
		sfree(key);
		goto failure;
	    }
	    comment = snewn(commlen + 1, char);
	    if (comment) {
		memcpy(comment, p, commlen);
		comment[commlen] = '\0';
	    }
	    key->comment = comment;

	    PUT_32BIT(ret, 1);
	    ret[4] = SSH_AGENT_FAILURE;
	    if (add234(ssh2keys, key) == key) {
		keylist_update();
		ret[4] = SSH_AGENT_SUCCESS;
	    } else {
		key->alg->freekey(key->data);
		sfree(key->comment);
		sfree(key);
	    }
	}
	break;
      case SSH1_AGENTC_REMOVE_RSA_IDENTITY:
	/*
	 * Remove from the list and return SSH_AGENT_SUCCESS, or
	 * perhaps SSH_AGENT_FAILURE if it wasn't in the list to
	 * start with.
	 */
	{
	    struct RSAKey reqkey, *key;
	    int n;

	    n = makekey(p, msgend - p, &reqkey, NULL, 0);
	    if (n < 0)
		goto failure;

	    key = find234(rsakeys, &reqkey, NULL);
	    freebn(reqkey.exponent);
	    freebn(reqkey.modulus);
	    PUT_32BIT(ret, 1);
	    ret[4] = SSH_AGENT_FAILURE;
	    if (key) {
		del234(rsakeys, key);
		keylist_update();
		freersakey(key);
		sfree(key);
		ret[4] = SSH_AGENT_SUCCESS;
	    }
	}
	break;
      case SSH2_AGENTC_REMOVE_IDENTITY:
	/*
	 * Remove from the list and return SSH_AGENT_SUCCESS, or
	 * perhaps SSH_AGENT_FAILURE if it wasn't in the list to
	 * start with.
	 */
	{
	    struct ssh2_userkey *key;
	    struct blob b;

	    if (msgend < p+4)
		goto failure;
	    b.len = toint(GET_32BIT(p));
	    p += 4;

	    if (b.len < 0 || b.len > msgend - p)
		goto failure;
	    b.blob = p;
	    p += b.len;

	    key = find234(ssh2keys, &b, cmpkeys_ssh2_asymm);
	    if (!key)
		goto failure;

	    PUT_32BIT(ret, 1);
	    ret[4] = SSH_AGENT_FAILURE;
	    if (key) {
		del234(ssh2keys, key);
		keylist_update();
		key->alg->freekey(key->data);
		sfree(key);
		ret[4] = SSH_AGENT_SUCCESS;
	    }
	}
	break;
      case SSH1_AGENTC_REMOVE_ALL_RSA_IDENTITIES:
	/*
	 * Remove all SSH-1 keys. Always returns success.
	 */
	{
	    struct RSAKey *rkey;

	    while ((rkey = index234(rsakeys, 0)) != NULL) {
		del234(rsakeys, rkey);
		freersakey(rkey);
		sfree(rkey);
	    }
	    keylist_update();

	    PUT_32BIT(ret, 1);
	    ret[4] = SSH_AGENT_SUCCESS;
	}
	break;
      case SSH2_AGENTC_REMOVE_ALL_IDENTITIES:
	/*
	 * Remove all SSH-2 keys. Always returns success.
	 */
	{
	    struct ssh2_userkey *skey;

	    while ((skey = index234(ssh2keys, 0)) != NULL) {
		del234(ssh2keys, skey);
		skey->alg->freekey(skey->data);
		sfree(skey);
	    }
	    keylist_update();

	    PUT_32BIT(ret, 1);
	    ret[4] = SSH_AGENT_SUCCESS;
	}
	break;
      default:
      failure:
	/*
	 * Unrecognised message. Return SSH_AGENT_FAILURE.
	 */
	PUT_32BIT(ret, 1);
	ret[4] = SSH_AGENT_FAILURE;
	break;
    }

    *outlen = 4 + GET_32BIT(ret);
    return ret;
}

void *pageant_failure_msg(int *outlen)
{
    unsigned char *ret = snewn(5, unsigned char);
    PUT_32BIT(ret, 1);
    ret[4] = SSH_AGENT_FAILURE;
    *outlen = 5;
    return ret;
}

void pageant_init(void)
{
    rsakeys = newtree234(cmpkeys_rsa);
    ssh2keys = newtree234(cmpkeys_ssh2);
}

struct RSAKey *pageant_nth_ssh1_key(int i)
{
    return index234(rsakeys, i);
}

struct ssh2_userkey *pageant_nth_ssh2_key(int i)
{
    return index234(ssh2keys, i);
}

int pageant_count_ssh1_keys(void)
{
    return count234(rsakeys);
}

int pageant_count_ssh2_keys(void)
{
    return count234(ssh2keys);
}

int pageant_add_ssh1_key(struct RSAKey *rkey)
{
    return add234(rsakeys, rkey) != rkey;
}

int pageant_add_ssh2_key(struct ssh2_userkey *skey)
{
    return add234(ssh2keys, skey) != skey;
}

int pageant_delete_ssh1_key(struct RSAKey *rkey)
{
    struct RSAKey *deleted = del234(rsakeys, rkey);
    if (!deleted)
        return FALSE;
    assert(deleted == rkey);
    return TRUE;
}

int pageant_delete_ssh2_key(struct ssh2_userkey *skey)
{
    struct ssh2_userkey *deleted = del234(ssh2keys, skey);
    if (!deleted)
        return FALSE;
    assert(deleted == skey);
    return TRUE;
}