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)

crypto/cms/cms.h

@@ -111,6 +111,7 @@ DECLARE_ASN1_PRINT_FUNCTION(CMS_ContentInfo)
 #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;
 		}
-
-
-	if (enc && !ec->key)
+	/* Generate random session key */
+	if (!enc || !ec->key)
 		{
-		/* Generate random key */
-		if (!ec->keylen)
-			ec->keylen = EVP_CIPHER_CTX_key_length(ctx);
-		ec->key = OPENSSL_malloc(ec->keylen);
-		if (!ec->key)
+		tkeylen = EVP_CIPHER_CTX_key_length(ctx);
+		tkey = OPENSSL_malloc(tkeylen);
+		if (!tkey)
 			{
 			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,
-				CMS_R_INVALID_KEY_LENGTH);
-			goto err;
+			/* Only reveal failure if debugging so we don't
+			 * leak information which may be useful in MMA.
+			 */
+			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

@@ -370,6 +370,8 @@ static int cms_RecipientInfo_ktri_decrypt(CMS_ContentInfo *cms,
 	unsigned char *ek = NULL;
 	size_t eklen;
 	int ret = 0;
+	CMS_EncryptedContentInfo *ec;
+	ec = cms->d.envelopedData->encryptedContentInfo;
 
 	if (ktri->pkey == NULL)
 		{
@@ -416,8 +418,14 @@ static int cms_RecipientInfo_ktri_decrypt(CMS_ContentInfo *cms,
 
 	ret = 1;
 
-	cms->d.envelopedData->encryptedContentInfo->key = ek;
-	cms->d.envelopedData->encryptedContentInfo->keylen = eklen;
+	if (ec->key)
+		{
+		OPENSSL_cleanse(ec->key, ec->keylen);
+		OPENSSL_free(ec->key);
+		}
+
+	ec->key = ek;
+	ec->keylen = eklen;
 
 	err:
 	if (pctx)

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

@@ -611,7 +611,10 @@ 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);
@@ -625,17 +628,38 @@ 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;
@@ -718,9 +742,14 @@ 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

@@ -204,11 +204,11 @@ static int pkcs7_decrypt_rinfo(unsigned char **pek, int *peklen,
 	unsigned char *ek = NULL;
 	size_t eklen;
 
-	int ret = 0;
+	int ret = -1;
 
 	pctx = EVP_PKEY_CTX_new(pkey, NULL);
 	if (!pctx)
-		return 0;
+		return -1;
 
 	if (EVP_PKEY_decrypt_init(pctx) <= 0)
 		goto err;
@@ -235,12 +235,19 @@ static int pkcs7_decrypt_rinfo(unsigned char **pek, int *peklen,
 	if (EVP_PKEY_decrypt(pctx, ek, &eklen,
 				ri->enc_key->data, ri->enc_key->length) <= 0)
 		{
+		ret = 0;
 		PKCS7err(PKCS7_F_PKCS7_DECRYPT_RINFO, ERR_R_EVP_LIB);
 		goto err;
 		}
 
 	ret = 1;
 
+	if (*pek)
+		{
+		OPENSSL_cleanse(*pek, *peklen);
+		OPENSSL_free(*pek);
+		}
+
 	*pek = ek;
 	*peklen = eklen;
 
@@ -500,8 +507,8 @@ BIO *PKCS7_dataDecode(PKCS7 *p7, EVP_PKEY *pkey, BIO *in_bio, X509 *pcert)
 		int max;
 		X509_OBJECT ret;
 #endif
-		unsigned char *ek = NULL;
-		int eklen;
+		unsigned char *ek = NULL, *tkey = NULL;
+		int eklen, tkeylen;
 
 		if ((etmp=BIO_new(BIO_f_cipher())) == NULL)
 			{
@@ -534,29 +541,28 @@ BIO *PKCS7_dataDecode(PKCS7 *p7, EVP_PKEY *pkey, BIO *in_bio, X509 *pcert)
 			}
 
 		/* If we haven't got a certificate try each ri in turn */
-
 		if (pcert == NULL)
 			{
+			/* Always attempt to decrypt all rinfo even
+			 * after sucess as a defence against MMA timing
+			 * attacks.
+			 */
 			for (i=0; i<sk_PKCS7_RECIP_INFO_num(rsk); i++)
 				{
 				ri=sk_PKCS7_RECIP_INFO_value(rsk,i);
+				
 				if (pkcs7_decrypt_rinfo(&ek, &eklen,
-							ri, pkey) > 0)
-					break;
+							ri, pkey) < 0)
+					goto err;
 				ERR_clear_error();
-				ri = NULL;
-				}
-			if (ri == NULL)
-				{
-				PKCS7err(PKCS7_F_PKCS7_DATADECODE,
-				      PKCS7_R_NO_RECIPIENT_MATCHES_KEY);
-				goto err;
 				}
 			}
 		else
 			{
-			if (pkcs7_decrypt_rinfo(&ek, &eklen, ri, pkey) <= 0)
+			/* Only exit on fatal errors, not decrypt failure */
+			if (pkcs7_decrypt_rinfo(&ek, &eklen, ri, pkey) < 0)
 				goto err;
+			ERR_clear_error();
 			}
 
 		evp_ctx=NULL;
@@ -565,6 +571,19 @@ 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 as MMA defence */
+		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 (ek == NULL)
+			{
+			ek = tkey;
+			eklen = tkeylen;
+			tkey = NULL;
+			}
 
 		if (eklen != EVP_CIPHER_CTX_key_length(evp_ctx)) {
 			/* Some S/MIME clients don't use the same key
@@ -573,11 +592,16 @@ BIO *PKCS7_dataDecode(PKCS7 *p7, EVP_PKEY *pkey, BIO *in_bio, X509 *pcert)
 			 */
 			if(!EVP_CIPHER_CTX_set_key_length(evp_ctx, eklen))
 				{
-				PKCS7err(PKCS7_F_PKCS7_DATADECODE,
-					PKCS7_R_DECRYPTED_KEY_IS_WRONG_LENGTH);
-				goto err;
+				/* Use random key as MMA defence */
+				OPENSSL_cleanse(ek, eklen);
+				OPENSSL_free(ek);
+				ek = tkey;
+				eklen = tkeylen;
+				tkey = NULL;
 				}
 		} 
+		/* Clear errors so we don't leak information useful in MMA */
+		ERR_clear_error();
 		if (EVP_CipherInit_ex(evp_ctx,NULL,NULL,ek,NULL,0) <= 0)
 			goto err;
 
@@ -586,6 +610,11 @@ BIO *PKCS7_dataDecode(PKCS7 *p7, EVP_PKEY *pkey, BIO *in_bio, X509 *pcert)
 			OPENSSL_cleanse(ek,eklen);
 			OPENSSL_free(ek);
 			}
+		if (tkey)
+			{
+			OPENSSL_cleanse(tkey,tkeylen);
+			OPENSSL_free(tkey);
+			}
 
 		if (out == NULL)
 			out=etmp;