Add support for a wolfSSL crypto backend. (#629)

It uses wolfSSL's OpenSSL compatibility layer, so rather than introduce new
wolfssl.h/c files, the new backend just reuses openssl.h/c. Additionally,
replace EVP_Cipher() calls with EVP_CipherUpdate(), since EVP_Cipher() is not
recommended.

Credit: Hayden Roche

Makefile.wolfSSL.inc

@@ -0,0 +1,3 @@
+CRYPTO_CSOURCES = openssl.c
+CRYPTO_HHEADERS = openssl.h
+CRYPTO_LTLIBS = -lwolfssl

acinclude.m4

@@ -431,6 +431,19 @@ m4_case([$1],
   ])
 ],
 
+[wolfssl], [
+  if test "${with_libwolfssl_prefix+set}" = set; then
+    CPPFLAGS="$CPPFLAGS${CPPFLAGS:+ }-I${with_libwolfssl_prefix}/include/wolfssl"
+  else
+    AC_MSG_ERROR([When using wolfSSL, must specify prefix with --with-libwolfssl-prefix in order to find OpenSSL compatibility headers.])
+  fi
+  LIBSSH2_LIB_HAVE_LINKFLAGS([wolfssl], [], [#include <wolfssl/options.h>], [
+    AC_DEFINE(LIBSSH2_WOLFSSL, 1, [Use $1])
+    LIBSREQUIRED="$LIBSREQUIRED${LIBSREQUIRED:+ }libwolfssl"
+    found_crypto="$1"
+  ])
+],
+
 [libgcrypt], [
   LIBSSH2_LIB_HAVE_LINKFLAGS([gcrypt], [], [#include <gcrypt.h>], [
     AC_DEFINE(LIBSSH2_LIBGCRYPT, 1, [Use $1])

configure.ac

@@ -92,6 +92,7 @@ m4_set_add([crypto_backends], [openssl])
 m4_set_add([crypto_backends], [libgcrypt])
 m4_set_add([crypto_backends], [mbedtls])
 m4_set_add([crypto_backends], [wincng])
+m4_set_add([crypto_backends], [wolfssl])
 
 AC_ARG_WITH([crypto],
   AC_HELP_STRING([--with-crypto=auto|]m4_set_contents([crypto_backends], [|]),

src/Makefile.am

@@ -5,6 +5,9 @@ AUTOMAKE_OPTIONS = foreign nostdinc
 if OPENSSL
 include ../Makefile.OpenSSL.inc
 endif
+if WOLFSSL
+include ../Makefile.wolfSSL.inc
+endif
 if LIBGCRYPT
 include ../Makefile.libgcrypt.inc
 endif

src/crypto.h

@@ -38,7 +38,7 @@
  * OF SUCH DAMAGE.
  */
 
-#ifdef LIBSSH2_OPENSSL
+#if defined(LIBSSH2_OPENSSL) || defined(LIBSSH2_WOLFSSL)
 #include "openssl.h"
 #endif
 

src/openssl.c

@@ -40,7 +40,8 @@
 
 #include "libssh2_priv.h"
 
-#ifdef LIBSSH2_OPENSSL /* compile only if we build with openssl */
+/* compile only if we build with openssl or wolfSSL */
+#if defined(LIBSSH2_OPENSSL) || defined(LIBSSH2_WOLFSSL)
 
 #include <string.h>
 #include "misc.h"
@@ -455,27 +456,20 @@ _libssh2_cipher_crypt(_libssh2_cipher_ctx * ctx,
 {
     unsigned char buf[EVP_MAX_BLOCK_LENGTH];
     int ret;
+    int outlen;
     (void) algo;
     (void) encrypt;
 
 #ifdef HAVE_OPAQUE_STRUCTS
-    ret = EVP_Cipher(*ctx, buf, block, blocksize);
+    ret = EVP_CipherUpdate(*ctx, buf, &outlen, block, blocksize);
 #else
-    ret = EVP_Cipher(ctx, buf, block, blocksize);
+    ret = EVP_CipherUpdate(ctx, buf, &outlen, block, blocksize);
 #endif
-#if defined(OPENSSL_VERSION_MAJOR) && OPENSSL_VERSION_MAJOR >= 3
-    if(ret != -1) {
-#else
     if(ret == 1) {
-#endif
         memcpy(block, buf, blocksize);
     }
 
-#if defined(OPENSSL_VERSION_MAJOR) && OPENSSL_VERSION_MAJOR >= 3
-    return ret != -1 ? 0 : 1;
-#else
     return ret == 1 ? 0 : 1;
-#endif
 }
 
 #if LIBSSH2_AES_CTR && !defined(HAVE_EVP_AES_128_CTR)

src/openssl.h

@@ -39,6 +39,43 @@
  * OF SUCH DAMAGE.
  */
 
+#ifdef LIBSSH2_WOLFSSL
+
+#include <wolfssl/options.h>
+#include <openssl/ecdh.h>
+
+#if defined(NO_DSA) || defined(HAVE_FIPS)
+#define OPENSSL_NO_DSA
+#endif
+
+#if defined(NO_MD5) || defined(HAVE_FIPS)
+#define OPENSSL_NO_MD5
+#endif
+
+#if !defined(WOLFSSL_RIPEMD) || defined(HAVE_FIPS)
+#define OPENSSL_NO_RIPEMD
+#endif
+
+#if defined(NO_RC4) || defined(HAVE_FIPS)
+#define OPENSSL_NO_RC4
+#endif
+
+#ifdef NO_DES3
+#define OPENSSL_NO_DES
+#endif
+
+#ifdef EVP_aes_128_ctr
+#define HAVE_EVP_AES_128_CTR
+#endif
+
+/* wolfSSL doesn't support Blowfish or CAST. */
+#define OPENSSL_NO_BF
+#define OPENSSL_NO_CAST
+/* wolfSSL has no engine framework. */
+#define OPENSSL_NO_ENGINE
+
+#endif /* LIBSSH2_WOLFSSL */
+
 #include <openssl/opensslconf.h>
 #include <openssl/sha.h>
 #include <openssl/rsa.h>
@@ -57,8 +94,10 @@
 #include <openssl/pem.h>
 #include <openssl/rand.h>
 
-#if OPENSSL_VERSION_NUMBER >= 0x10100000L && \
+#if (OPENSSL_VERSION_NUMBER >= 0x10100000L && \
-    !defined(LIBRESSL_VERSION_NUMBER)
+    !defined(LIBRESSL_VERSION_NUMBER)) || defined(LIBSSH2_WOLFSSL)
+/* For wolfSSL, whether the structs are truly opaque or not, it's best to not
+ * rely on their internal data members being exposed publicly. */
 # define HAVE_OPAQUE_STRUCTS 1
 #endif
 
@@ -105,7 +144,8 @@
 #define LIBSSH2_HMAC_SHA256 1
 #define LIBSSH2_HMAC_SHA512 1
 
-#if OPENSSL_VERSION_NUMBER >= 0x00907000L && !defined(OPENSSL_NO_AES)
+#if (OPENSSL_VERSION_NUMBER >= 0x00907000L && !defined(OPENSSL_NO_AES)) || \
+    (defined(LIBSSH2_WOLFSSL) && defined(WOLFSSL_AES_COUNTER))
 # define LIBSSH2_AES_CTR 1
 # define LIBSSH2_AES 1
 #else