Fix for CMS/PKCS7 MMA. If RSA decryption fails use a random key and

continue with symmetric decryption process to avoid leaking timing
information to an attacker.

Thanks to Ivan Nestlerode <inestlerode@us.ibm.com> for discovering
this issue. (CVE-2012-0884)

CHANGES

@@ -4,6 +4,17 @@
 
  Changes between 0.9.8t and 0.9.8u [xx XXX xxxx]
 
+  *) Fix MMA (Bleichenbacher's attack on PKCS #1 v1.5 RSA padding) weakness
+     in CMS and PKCS7 code. When RSA decryption fails use a random key for
+     content decryption and always return the same error. Note: this attack
+     needs on average 2^20 messages so it only affects automated senders. The
+     old behaviour can be reenabled in the CMS code by setting the
+     CMS_DEBUG_DECRYPT flag: this is useful for debugging and testing where
+     an MMA defence is not necessary.
+     Thanks to Ivan Nestlerode <inestlerode@us.ibm.com> for discovering
+     this issue. (CVE-2012-0884)
+     [Steve Henson]
+
   *) Fix CVE-2011-4619: make sure we really are receiving a 
      client hello before rejecting multiple SGC restarts. Thanks to
      Ivan Nestlerode <inestlerode@us.ibm.com> for discovering this bug.

apps/cms.c

@@ -226,6 +226,8 @@ int MAIN(int argc, char **argv)
 		else if (!strcmp(*args,"-camellia256"))
 				cipher = EVP_camellia_256_cbc();
 #endif
+		else if (!strcmp (*args, "-debug_decrypt")) 
+				flags |= CMS_DEBUG_DECRYPT;
 		else if (!strcmp (*args, "-text")) 
 				flags |= CMS_TEXT;
 		else if (!strcmp (*args, "-nointern")) 
@@ -1013,6 +1015,8 @@ int MAIN(int argc, char **argv)
 	ret = 4;
 	if (operation == SMIME_DECRYPT)
 		{
+		if (flags & CMS_DEBUG_DECRYPT)
+			CMS_decrypt(cms, NULL, NULL, NULL, NULL, flags);
 
 		if (secret_key)
 			{

crypto/cms/cms.h

@@ -110,6 +110,7 @@ DECLARE_ASN1_FUNCTIONS_const(CMS_ReceiptRequest)
 #define CMS_PARTIAL			0x4000
 #define CMS_REUSE_DIGEST		0x8000
 #define CMS_USE_KEYID			0x10000
+#define CMS_DEBUG_DECRYPT		0x20000
 
 const ASN1_OBJECT *CMS_get0_type(CMS_ContentInfo *cms);
 

crypto/cms/cms_enc.c

@@ -73,6 +73,8 @@ BIO *cms_EncryptedContent_init_bio(CMS_EncryptedContentInfo *ec)
 	const EVP_CIPHER *ciph;
 	X509_ALGOR *calg = ec->contentEncryptionAlgorithm;
 	unsigned char iv[EVP_MAX_IV_LENGTH], *piv = NULL;
+	unsigned char *tkey = NULL;
+	size_t tkeylen;
 
 	int ok = 0;
 
@@ -137,32 +139,57 @@ BIO *cms_EncryptedContent_init_bio(CMS_EncryptedContentInfo *ec)
 				CMS_R_CIPHER_PARAMETER_INITIALISATION_ERROR);
 		goto err;
 		}
-
+	/* Generate random session key */
-
+	if (!enc || !ec->key)
-	if (enc && !ec->key)
 		{
-		/* Generate random key */
+		tkeylen = EVP_CIPHER_CTX_key_length(ctx);
-		if (!ec->keylen)
+		tkey = OPENSSL_malloc(tkeylen);
-			ec->keylen = EVP_CIPHER_CTX_key_length(ctx);
+		if (!tkey)
-		ec->key = OPENSSL_malloc(ec->keylen);
-		if (!ec->key)
 			{
 			CMSerr(CMS_F_CMS_ENCRYPTEDCONTENT_INIT_BIO,
 							ERR_R_MALLOC_FAILURE);
 			goto err;
 			}
-		if (EVP_CIPHER_CTX_rand_key(ctx, ec->key) <= 0)
+		if (EVP_CIPHER_CTX_rand_key(ctx, tkey) <= 0)
 			goto err;
-		keep_key = 1;
 		}
-	else if (ec->keylen != (unsigned int)EVP_CIPHER_CTX_key_length(ctx))
+
+	if (!ec->key)
+		{
+		ec->key = tkey;
+		ec->keylen = tkeylen;
+		tkey = NULL;
+		if (enc)
+			keep_key = 1;
+		else
+			ERR_clear_error();
+		
+		}
+
+	if (ec->keylen != tkeylen)
 		{
 		/* If necessary set key length */
 		if (EVP_CIPHER_CTX_set_key_length(ctx, ec->keylen) <= 0)
 			{
-			CMSerr(CMS_F_CMS_ENCRYPTEDCONTENT_INIT_BIO,
+			/* Only reveal failure if debugging so we don't
-				CMS_R_INVALID_KEY_LENGTH);
+			 * leak information which may be useful in MMA.
-			goto err;
+			 */
+			if (ec->debug)
+				{
+				CMSerr(CMS_F_CMS_ENCRYPTEDCONTENT_INIT_BIO,
+						CMS_R_INVALID_KEY_LENGTH);
+				goto err;
+				}
+			else
+				{
+				/* Use random key */
+				OPENSSL_cleanse(ec->key, ec->keylen);
+				OPENSSL_free(ec->key);
+				ec->key = tkey;
+				ec->keylen = tkeylen;
+				tkey = NULL;
+				ERR_clear_error();
+				}
 			}
 		}
 
@@ -198,6 +225,11 @@ BIO *cms_EncryptedContent_init_bio(CMS_EncryptedContentInfo *ec)
 		OPENSSL_free(ec->key);
 		ec->key = NULL;
 		}
+	if (tkey)
+		{
+		OPENSSL_cleanse(tkey, tkeylen);
+		OPENSSL_free(tkey);
+		}
 	if (ok)
 		return b;
 	BIO_free(b);

crypto/cms/cms_env.c

@@ -352,6 +352,8 @@ static int cms_RecipientInfo_ktri_decrypt(CMS_ContentInfo *cms,
 	unsigned char *ek = NULL;
 	int eklen;
 	int ret = 0;
+	CMS_EncryptedContentInfo *ec;
+	ec = cms->d.envelopedData->encryptedContentInfo;
 
 	if (ktri->pkey == NULL)
 		{
@@ -382,8 +384,14 @@ static int cms_RecipientInfo_ktri_decrypt(CMS_ContentInfo *cms,
 
 	ret = 1;
 
-	cms->d.envelopedData->encryptedContentInfo->key = ek;
+	if (ec->key)
-	cms->d.envelopedData->encryptedContentInfo->keylen = eklen;
+		{
+		OPENSSL_cleanse(ec->key, ec->keylen);
+		OPENSSL_free(ec->key);
+		}
+
+	ec->key = ek;
+	ec->keylen = eklen;
 
 	err:
 	if (!ret && ek)

crypto/cms/cms_lcl.h

@@ -175,6 +175,8 @@ struct CMS_EncryptedContentInfo_st
 	const EVP_CIPHER *cipher;
 	unsigned char *key;
 	size_t keylen;
+	/* Set to 1 if we are debugging decrypt and don't fake keys for MMA */
+	int debug;
 	};
 
 struct CMS_RecipientInfo_st

crypto/cms/cms_smime.c

@@ -622,7 +622,10 @@ int CMS_decrypt_set1_pkey(CMS_ContentInfo *cms, EVP_PKEY *pk, X509 *cert)
 	STACK_OF(CMS_RecipientInfo) *ris;
 	CMS_RecipientInfo *ri;
 	int i, r;
+	int debug = 0;
 	ris = CMS_get0_RecipientInfos(cms);
+	if (ris)
+		debug = cms->d.envelopedData->encryptedContentInfo->debug;
 	for (i = 0; i < sk_CMS_RecipientInfo_num(ris); i++)
 		{
 		ri = sk_CMS_RecipientInfo_value(ris, i);
@@ -636,17 +639,38 @@ int CMS_decrypt_set1_pkey(CMS_ContentInfo *cms, EVP_PKEY *pk, X509 *cert)
 			CMS_RecipientInfo_set0_pkey(ri, pk);
 			r = CMS_RecipientInfo_decrypt(cms, ri);
 			CMS_RecipientInfo_set0_pkey(ri, NULL);
-			if (r > 0)
-				return 1;
 			if (cert)
 				{
+				/* If not debugging clear any error and
+				 * return success to avoid leaking of
+				 * information useful to MMA
+				 */
+				if (!debug)
+					{
+					ERR_clear_error();
+					return 1;
+					}
+				if (r > 0)
+					return 1;
 				CMSerr(CMS_F_CMS_DECRYPT_SET1_PKEY,
 						CMS_R_DECRYPT_ERROR);
 				return 0;
 				}
-			ERR_clear_error();
+			/* If no cert and not debugging don't leave loop
+			 * after first successful decrypt. Always attempt
+			 * to decrypt all recipients to avoid leaking timing
+			 * of a successful decrypt.
+			 */
+			else if (r > 0 && debug)
+				return 1;
 			}
 		}
+	/* If no cert and not debugging always return success */
+	if (!cert && !debug)
+		{
+		ERR_clear_error();
+		return 1;
+		}
 
 	CMSerr(CMS_F_CMS_DECRYPT_SET1_PKEY, CMS_R_NO_MATCHING_RECIPIENT);
 	return 0;
@@ -705,9 +729,14 @@ int CMS_decrypt(CMS_ContentInfo *cms, EVP_PKEY *pk, X509 *cert,
 		}
 	if (!dcont && !check_content(cms))
 		return 0;
+	if (flags & CMS_DEBUG_DECRYPT)
+		cms->d.envelopedData->encryptedContentInfo->debug = 1;
+	else
+		cms->d.envelopedData->encryptedContentInfo->debug = 0;
+	if (!pk && !cert && !dcont && !out)
+		return 1;
 	if (pk && !CMS_decrypt_set1_pkey(cms, pk, cert))
 		return 0;
-
 	cont = CMS_dataInit(cms, dcont);
 	if (!cont)
 		return 0;

crypto/pkcs7/pk7_doit.c

@@ -420,6 +420,8 @@ BIO *PKCS7_dataDecode(PKCS7 *p7, EVP_PKEY *pkey, BIO *in_bio, X509 *pcert)
 		int max;
 		X509_OBJECT ret;
 #endif
+		unsigned char *tkey = NULL;
+		int tkeylen;
 		int jj;
 
 		if ((etmp=BIO_new(BIO_f_cipher())) == NULL)
@@ -461,36 +463,42 @@ BIO *PKCS7_dataDecode(PKCS7 *p7, EVP_PKEY *pkey, BIO *in_bio, X509 *pcert)
 
 		if (pcert == NULL)
 			{
+			/* Temporary storage in case EVP_PKEY_decrypt
+			 * overwrites output buffer on error.
+			 */
+			unsigned char *tmp2;
+			tmp2 = OPENSSL_malloc(jj);
+			if (!tmp2)
+				goto err;
+			jj = -1;
+			/* Always attempt to decrypt all cases to avoid
+			 * leaking timing information about a successful
+			 * decrypt.
+			 */
 			for (i=0; i<sk_PKCS7_RECIP_INFO_num(rsk); i++)
 				{
+				int tret;
 				ri=sk_PKCS7_RECIP_INFO_value(rsk,i);
-				jj=EVP_PKEY_decrypt(tmp,
+				tret=EVP_PKEY_decrypt(tmp2,
 					M_ASN1_STRING_data(ri->enc_key),
 					M_ASN1_STRING_length(ri->enc_key),
 						pkey);
-				if (jj > 0)
+				if (tret > 0)
-					break;
+					{
+					memcpy(tmp, tmp2, tret);
+					OPENSSL_cleanse(tmp2, tret);
+					jj = tret;
+					}
 				ERR_clear_error();
-				ri = NULL;
-				}
-			if (ri == NULL)
-				{
-				PKCS7err(PKCS7_F_PKCS7_DATADECODE,
-				      PKCS7_R_NO_RECIPIENT_MATCHES_KEY);
-				goto err;
 				}
+			OPENSSL_free(tmp2);
 			}
 		else
 			{
 			jj=EVP_PKEY_decrypt(tmp,
 				M_ASN1_STRING_data(ri->enc_key),
 				M_ASN1_STRING_length(ri->enc_key), pkey);
-			if (jj <= 0)
+			ERR_clear_error();
-				{
-				PKCS7err(PKCS7_F_PKCS7_DATADECODE,
-								ERR_R_EVP_LIB);
-				goto err;
-				}
 			}
 
 		evp_ctx=NULL;
@@ -499,24 +507,49 @@ BIO *PKCS7_dataDecode(PKCS7 *p7, EVP_PKEY *pkey, BIO *in_bio, X509 *pcert)
 			goto err;
 		if (EVP_CIPHER_asn1_to_param(evp_ctx,enc_alg->parameter) < 0)
 			goto err;
+		/* Generate random key to counter MMA */
+		tkeylen = EVP_CIPHER_CTX_key_length(evp_ctx);
+		tkey = OPENSSL_malloc(tkeylen);
+		if (!tkey)
+			goto err;
+		if (EVP_CIPHER_CTX_rand_key(evp_ctx, tkey) <= 0)
+			goto err;
+		/* If we have no key use random key */
+		if (jj <= 0)
+			{
+			OPENSSL_free(tmp);
+			jj = tkeylen;
+			tmp = tkey;
+			tkey = NULL;
+			}
 
-		if (jj != EVP_CIPHER_CTX_key_length(evp_ctx)) {
+		if (jj != tkeylen) {
 			/* Some S/MIME clients don't use the same key
 			 * and effective key length. The key length is
 			 * determined by the size of the decrypted RSA key.
 			 */
 			if(!EVP_CIPHER_CTX_set_key_length(evp_ctx, jj))
 				{
-				PKCS7err(PKCS7_F_PKCS7_DATADECODE,
+				/* As MMA defence use random key instead */
-					PKCS7_R_DECRYPTED_KEY_IS_WRONG_LENGTH);
+				OPENSSL_cleanse(tmp, jj);
-				goto err;
+				OPENSSL_free(tmp);
+				jj = tkeylen;
+				tmp = tkey;
+				tkey = NULL;
 				}
 		} 
+		ERR_clear_error();
 		if (EVP_CipherInit_ex(evp_ctx,NULL,NULL,tmp,NULL,0) <= 0)
 			goto err;
 
 		OPENSSL_cleanse(tmp,jj);
 
+		if (tkey)
+			{
+			OPENSSL_cleanse(tkey, tkeylen);
+			OPENSSL_free(tkey);
+			}
+
 		if (out == NULL)
 			out=etmp;
 		else