smimeutil.c

来自「支持SSL v2/v3, TLS, PKCS #5, PKCS #7, PKCS」· C语言 代码 · 共 715 行 · 第 1/2 页

 * smime_choose_cipher - choose a cipher that works for all the recipients
 *
 * "scert"  - sender's certificate
 * "rcerts" - recipient's certificates
 */
static long
smime_choose_cipher(CERTCertificate *scert, CERTCertificate **rcerts)
{
    PRArenaPool *poolp;
    long cipher;
    long chosen_cipher;
    int *cipher_abilities;
    int *cipher_votes;
    int weak_mapi;
    int strong_mapi;
    int rcount, mapi, max, i;
    PRBool scert_is_fortezza = (scert == NULL) ? PR_FALSE : PK11_FortezzaHasKEA(scert);

    chosen_cipher = SMIME_RC2_CBC_40;		/* the default, LCD */
    weak_mapi = smime_mapi_by_cipher(chosen_cipher);

    poolp = PORT_NewArena (1024);		/* XXX what is right value? */
    if (poolp == NULL)
	goto done;

    cipher_abilities = (int *)PORT_ArenaZAlloc(poolp, smime_cipher_map_count * sizeof(int));
    cipher_votes     = (int *)PORT_ArenaZAlloc(poolp, smime_cipher_map_count * sizeof(int));
    if (cipher_votes == NULL || cipher_abilities == NULL)
	goto done;

    /* If the user has the Fortezza preference turned on, make
     *  that the strong cipher. Otherwise, use triple-DES. */
    strong_mapi = smime_mapi_by_cipher (SMIME_DES_EDE3_168);
    if (scert_is_fortezza) {
	mapi = smime_mapi_by_cipher(SMIME_FORTEZZA);
	if (mapi >= 0 && smime_cipher_map[mapi].enabled)
	    strong_mapi = mapi;
    }

    /* walk all the recipient's certs */
    for (rcount = 0; rcerts[rcount] != NULL; rcount++) {
	SECItem *profile;
	NSSSMIMECapability **caps;
	int pref;

	/* the first cipher that matches in the user's SMIME profile gets
	 * "smime_cipher_map_count" votes; the next one gets "smime_cipher_map_count" - 1
	 * and so on. If every cipher matches, the last one gets 1 (one) vote */
	pref = smime_cipher_map_count;

	/* find recipient's SMIME profile */
	profile = CERT_FindSMimeProfile(rcerts[rcount]);

	if (profile != NULL && profile->data != NULL && profile->len > 0) {
	    /* we have a profile (still DER-encoded) */
	    caps = NULL;
	    /* decode it */
	    if (SEC_ASN1DecodeItem(poolp, &caps, NSSSMIMECapabilitiesTemplate, profile) == SECSuccess &&
		    caps != NULL)
	    {
		/* walk the SMIME capabilities for this recipient */
		for (i = 0; caps[i] != NULL; i++) {
		    cipher = nss_SMIME_FindCipherForSMIMECap(caps[i]);
		    mapi = smime_mapi_by_cipher(cipher);
		    if (mapi >= 0) {
			/* found the cipher */
			cipher_abilities[mapi]++;
			cipher_votes[mapi] += pref;
			--pref;
		    }
		}
	    }
	} else {
	    /* no profile found - so we can only assume that the user can do
	     * the mandatory algorithms which is RC2-40 (weak crypto) and 3DES (strong crypto) */
	    SECKEYPublicKey *key;
	    unsigned int pklen_bits;

	    /*
	     * if recipient's public key length is > 512, vote for a strong cipher
	     * please not that the side effect of this is that if only one recipient
	     * has an export-level public key, the strong cipher is disabled.
	     *
	     * XXX This is probably only good for RSA keys.  What I would
	     * really like is a function to just say;  Is the public key in
	     * this cert an export-length key?  Then I would not have to
	     * know things like the value 512, or the kind of key, or what
	     * a subjectPublicKeyInfo is, etc.
	     */
	    key = CERT_ExtractPublicKey(rcerts[rcount]);
	    pklen_bits = 0;
	    if (key != NULL) {
		pklen_bits = SECKEY_PublicKeyStrength (key) * 8;
		SECKEY_DestroyPublicKey (key);
	    }

	    if (pklen_bits > 512) {
		/* cast votes for the strong algorithm */
		cipher_abilities[strong_mapi]++;
		cipher_votes[strong_mapi] += pref;
		pref--;
	    } 

	    /* always cast (possibly less) votes for the weak algorithm */
	    cipher_abilities[weak_mapi]++;
	    cipher_votes[weak_mapi] += pref;
	}
	if (profile != NULL)
	    SECITEM_FreeItem(profile, PR_TRUE);
    }

    /* find cipher that is agreeable by all recipients and that has the most votes */
    max = 0;
    for (mapi = 0; mapi < smime_cipher_map_count; mapi++) {
	/* if not all of the recipients can do this, forget it */
	if (cipher_abilities[mapi] != rcount)
	    continue;
	/* if cipher is not enabled or not allowed by policy, forget it */
	if (!smime_cipher_map[mapi].enabled || !smime_cipher_map[mapi].allowed)
	    continue;
	/* if we're not doing fortezza, but the cipher is fortezza, forget it */
	if (!scert_is_fortezza  && (smime_cipher_map[mapi].cipher == SMIME_FORTEZZA))
	    continue;
	/* now see if this one has more votes than the last best one */
	if (cipher_votes[mapi] >= max) {
	    /* if equal number of votes, prefer the ones further down in the list */
	    /* with the expectation that these are higher rated ciphers */
	    chosen_cipher = smime_cipher_map[mapi].cipher;
	    max = cipher_votes[mapi];
	}
    }
    /* if no common cipher was found, chosen_cipher stays at the default */

done:
    if (poolp != NULL)
	PORT_FreeArena (poolp, PR_FALSE);

    return chosen_cipher;
}

/*
 * XXX This is a hack for now to satisfy our current interface.
 * Eventually, with more parameters needing to be specified, just
 * looking up the keysize is not going to be sufficient.
 */
static int
smime_keysize_by_cipher (unsigned long which)
{
    int keysize;

    switch (which) {
      case SMIME_RC2_CBC_40:
	keysize = 40;
	break;
      case SMIME_RC2_CBC_64:
	keysize = 64;
	break;
      case SMIME_RC2_CBC_128:
	keysize = 128;
	break;
      case SMIME_DES_CBC_56:
      case SMIME_DES_EDE3_168:
      case SMIME_FORTEZZA:
	/*
	 * These are special; since the key size is fixed, we actually
	 * want to *avoid* specifying a key size.
	 */
	keysize = 0;
	break;
      default:
	keysize = -1;
	break;
    }

    return keysize;
}

/*
 * NSS_SMIMEUtil_FindBulkAlgForRecipients - find bulk algorithm suitable for all recipients
 *
 * it would be great for UI purposes if there would be a way to find out which recipients
 * prevented a strong cipher from being used...
 */
SECStatus
NSS_SMIMEUtil_FindBulkAlgForRecipients(CERTCertificate **rcerts, SECOidTag *bulkalgtag, int *keysize)
{
    unsigned long cipher;
    int mapi;

    cipher = smime_choose_cipher(NULL, rcerts);
    mapi = smime_mapi_by_cipher(cipher);

    *bulkalgtag = smime_cipher_map[mapi].algtag;
    *keysize = smime_keysize_by_cipher(smime_cipher_map[mapi].algtag);

    return SECSuccess;
}

/*
 * NSS_SMIMEUtil_CreateSMIMECapabilities - get S/MIME capabilities for this instance of NSS
 *
 * scans the list of allowed and enabled ciphers and construct a PKCS9-compliant
 * S/MIME capabilities attribute value.
 *
 * XXX Please note that, in contradiction to RFC2633 2.5.2, the capabilities only include
 * symmetric ciphers, NO signature algorithms or key encipherment algorithms.
 *
 * "poolp" - arena pool to create the S/MIME capabilities data on
 * "dest" - SECItem to put the data in
 * "includeFortezzaCiphers" - PR_TRUE if fortezza ciphers should be included
 */
SECStatus
NSS_SMIMEUtil_CreateSMIMECapabilities(PLArenaPool *poolp, SECItem *dest, PRBool includeFortezzaCiphers)
{
    NSSSMIMECapability *cap;
    NSSSMIMECapability **smime_capabilities;
    smime_cipher_map_entry *map;
    SECOidData *oiddata;
    SECItem *dummy;
    int i, capIndex;

    /* if we have an old NSSSMIMECapability array, we'll reuse it (has the right size) */
    /* smime_cipher_map_count + 1 is an upper bound - we might end up with less */
    smime_capabilities = (NSSSMIMECapability **)PORT_ZAlloc((smime_cipher_map_count + 1)
				      * sizeof(NSSSMIMECapability *));
    if (smime_capabilities == NULL)
	return SECFailure;

    capIndex = 0;

    /* Add all the symmetric ciphers
     * We walk the cipher list backwards, as it is ordered by increasing strength,
     * we prefer the stronger cipher over a weaker one, and we have to list the
     * preferred algorithm first */
    for (i = smime_cipher_map_count - 1; i >= 0; i--) {
	/* Find the corresponding entry in the cipher map. */
	map = &(smime_cipher_map[i]);
	if (!map->enabled)
	    continue;

	/* If we're using a non-Fortezza cert, only advertise non-Fortezza
	   capabilities. (We advertise all capabilities if we have a 
	   Fortezza cert.) */
	if ((!includeFortezzaCiphers) && (map->cipher == SMIME_FORTEZZA))
	    continue;

	/* get next SMIME capability */
	cap = (NSSSMIMECapability *)PORT_ZAlloc(sizeof(NSSSMIMECapability));
	if (cap == NULL)
	    break;
	smime_capabilities[capIndex++] = cap;

	oiddata = SECOID_FindOIDByTag(map->algtag);
	if (oiddata == NULL)
	    break;

	cap->capabilityID.data = oiddata->oid.data;
	cap->capabilityID.len = oiddata->oid.len;
	cap->parameters.data = map->parms ? map->parms->data : NULL;
	cap->parameters.len = map->parms ? map->parms->len : 0;
	cap->cipher = smime_cipher_map[i].cipher;
    }

    /* XXX add signature algorithms */
    /* XXX add key encipherment algorithms */

    smime_capabilities[capIndex] = NULL;	/* last one - now encode */
    dummy = SEC_ASN1EncodeItem(poolp, dest, &smime_capabilities, NSSSMIMECapabilitiesTemplate);

    /* now that we have the proper encoded SMIMECapabilities (or not),
     * free the work data */
    for (i = 0; smime_capabilities[i] != NULL; i++)
	PORT_Free(smime_capabilities[i]);
    PORT_Free(smime_capabilities);

    return (dummy == NULL) ? SECFailure : SECSuccess;
}

/*
 * NSS_SMIMEUtil_CreateSMIMEEncKeyPrefs - create S/MIME encryption key preferences attr value
 *
 * "poolp" - arena pool to create the attr value on
 * "dest" - SECItem to put the data in
 * "cert" - certificate that should be marked as preferred encryption key
 *          cert is expected to have been verified for EmailRecipient usage.
 */
SECStatus
NSS_SMIMEUtil_CreateSMIMEEncKeyPrefs(PLArenaPool *poolp, SECItem *dest, CERTCertificate *cert)
{
    NSSSMIMEEncryptionKeyPreference ekp;
    SECItem *dummy = NULL;
    PLArenaPool *tmppoolp;

    if (cert == NULL)
	goto loser;

    tmppoolp = PORT_NewArena(1024);
    if (tmppoolp == NULL)
	goto loser;

    /* XXX hardcoded IssuerSN choice for now */
    ekp.selector = NSSSMIMEEncryptionKeyPref_IssuerSN;
    ekp.id.issuerAndSN = CERT_GetCertIssuerAndSN(tmppoolp, cert);
    if (ekp.id.issuerAndSN == NULL)
	goto loser;

    dummy = SEC_ASN1EncodeItem(poolp, dest, &ekp, smime_encryptionkeypref_template);

loser:
    if (tmppoolp) PORT_FreeArena(tmppoolp, PR_FALSE);

    return (dummy == NULL) ? SECFailure : SECSuccess;
}

/*
 * NSS_SMIMEUtil_GetCertFromEncryptionKeyPreference -
 *				find cert marked by EncryptionKeyPreference attribute
 *
 * "certdb" - handle for the cert database to look in
 * "DERekp" - DER-encoded value of S/MIME Encryption Key Preference attribute
 *
 * if certificate is supposed to be found among the message's included certificates,
 * they are assumed to have been imported already.
 */
CERTCertificate *
NSS_SMIMEUtil_GetCertFromEncryptionKeyPreference(CERTCertDBHandle *certdb, SECItem *DERekp)
{
    PLArenaPool *tmppoolp = NULL;
    CERTCertificate *cert = NULL;
    NSSSMIMEEncryptionKeyPreference ekp;

    tmppoolp = PORT_NewArena(1024);
    if (tmppoolp == NULL)
	return NULL;

    /* decode DERekp */
    if (SEC_ASN1DecodeItem(tmppoolp, &ekp, smime_encryptionkeypref_template, DERekp) != SECSuccess)
	goto loser;

    /* find cert */
    switch (ekp.selector) {
    case NSSSMIMEEncryptionKeyPref_IssuerSN:
	cert = CERT_FindCertByIssuerAndSN(certdb, ekp.id.issuerAndSN);
	break;
    case NSSSMIMEEncryptionKeyPref_RKeyID:
    case NSSSMIMEEncryptionKeyPref_SubjectKeyID:
	/* XXX not supported yet - we need to be able to look up certs by SubjectKeyID */
	break;
    default:
	PORT_Assert(0);
    }
loser:
    if (tmppoolp) PORT_FreeArena(tmppoolp, PR_FALSE);

    return cert;
}