Revert "RT3425: constant-time evp_enc"

Causes more problems than it fixes: even though error codes
are not part of the stable API, several users rely on the
specific error code, and the change breaks them. Conversely,
we don't have any concrete use-cases for constant-time behaviour here.

This reverts commit 4aac102f.
Reviewed-by: NAndy Polyakov <appro@openssl.org>

crypto/evp/Makefile

@@ -406,7 +406,7 @@ evp_enc.o: ../../include/openssl/pkcs7.h ../../include/openssl/rand.h
 evp_enc.o: ../../include/openssl/safestack.h ../../include/openssl/sha.h
 evp_enc.o: ../../include/openssl/stack.h ../../include/openssl/symhacks.h
 evp_enc.o: ../../include/openssl/x509.h ../../include/openssl/x509_vfy.h
-evp_enc.o: ../constant_time_locl.h ../cryptlib.h evp_enc.c evp_locl.h
+evp_enc.o: ../cryptlib.h evp_enc.c evp_locl.h
 evp_err.o: ../../include/openssl/asn1.h ../../include/openssl/bio.h
 evp_err.o: ../../include/openssl/crypto.h ../../include/openssl/e_os2.h
 evp_err.o: ../../include/openssl/err.h ../../include/openssl/evp.h

crypto/evp/evp_enc.c

@@ -64,7 +64,6 @@
 #ifndef OPENSSL_NO_ENGINE
 #include <openssl/engine.h>
 #endif
-#include "constant_time_locl.h"
 #include "evp_locl.h"
 
 const char EVP_version[]="EVP" OPENSSL_VERSION_PTEXT;
@@ -492,21 +491,21 @@ int EVP_DecryptFinal(EVP_CIPHER_CTX *ctx, unsigned char *out, int *outl)
 
 int EVP_DecryptFinal_ex(EVP_CIPHER_CTX *ctx, unsigned char *out, int *outl)
 	{
-	unsigned int i, b;
-        unsigned char pad, padding_good;
+	int i,n;
+	unsigned int b;
 	*outl=0;
 
 	if (ctx->cipher->flags & EVP_CIPH_FLAG_CUSTOM_CIPHER)
 		{
-		int ret = ctx->cipher->do_cipher(ctx, out, NULL, 0);
-		if (ret < 0)
+		i = ctx->cipher->do_cipher(ctx, out, NULL, 0);
+		if (i < 0)
 			return 0;
 		else
-			*outl = ret;
+			*outl = i;
 		return 1;
 		}
 
-	b=(unsigned int)(ctx->cipher->block_size);
+	b=ctx->cipher->block_size;
 	if (ctx->flags & EVP_CIPH_NO_PADDING)
 		{
 		if(ctx->buf_len)
@@ -525,34 +524,28 @@ int EVP_DecryptFinal_ex(EVP_CIPHER_CTX *ctx, unsigned char *out, int *outl)
 			return(0);
 			}
 		OPENSSL_assert(b <= sizeof ctx->final);
-		pad=ctx->final[b-1];
-
-		padding_good = (unsigned char)(~constant_time_is_zero_8(pad));
-		padding_good &= constant_time_ge_8(b, pad);
-
-                for (i = 1; i < b; ++i)
+		n=ctx->final[b-1];
+		if (n == 0 || n > (int)b)
 			{
-			unsigned char is_pad_index = constant_time_lt_8(i, pad);
-			unsigned char pad_byte_good = constant_time_eq_8(ctx->final[b-i-1], pad);
-			padding_good &= constant_time_select_8(is_pad_index, pad_byte_good, 0xff);
+			EVPerr(EVP_F_EVP_DECRYPTFINAL_EX,EVP_R_BAD_DECRYPT);
+			return(0);
 			}
-
-		/*
-		 * At least 1 byte is always padding, so we always write b - 1
-		 * bytes to avoid a timing leak. The caller is required to have |b|
-		 * bytes space in |out| by the API contract.
-		 */
-		for (i = 0; i < b - 1; ++i)
-			out[i] = ctx->final[i] & padding_good;
-		/* Safe cast: for a good padding, EVP_MAX_IV_LENGTH >= b >= pad */
-		*outl = padding_good & ((unsigned char)(b - pad));
-		return padding_good & 1;
+		for (i=0; i<n; i++)
+			{
+			if (ctx->final[--b] != n)
+				{
+				EVPerr(EVP_F_EVP_DECRYPTFINAL_EX,EVP_R_BAD_DECRYPT);
+				return(0);
+				}
+			}
+		n=ctx->cipher->block_size-n;
+		for (i=0; i<n; i++)
+			out[i]=ctx->final[i];
+		*outl=n;
 		}
 	else
-		{
-		*outl = 0;
-		return 1;
-		}
+		*outl=0;
+	return(1);
 	}
 
 void EVP_CIPHER_CTX_free(EVP_CIPHER_CTX *ctx)