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From 4f7ab2040bb71f03a8f8388911144559aa2a5b60 Mon Sep 17 00:00:00 2001
From: Eneas U de Queiroz <cote2004-github@yahoo.com>
Date: Thu, 27 Sep 2018 08:44:39 -0300
Subject: Add OPENSSL_PREFER_CHACHA_OVER_GCM option
This enables a compile-time option to prefer ChaCha20-Poly1305 over
AES-GCM in the openssl default ciphersuite, which is useful in systems
without AES specific CPU instructions.
OPENSSL_PREFER_CHACHA_OVER_GCM must be defined to enable it.
Note that this does not have the same effect as the
SL_OP_PRIORITIZE_CHACHA option, which prioritizes ChaCha20-Poly1305 only
when the client has it on top of its ciphersuite preference.
Signed-off-by: Eneas U de Queiroz <cote2004-github@yahoo.com>
diff --git a/include/openssl/ssl.h b/include/openssl/ssl.h
index 6724ccf2d2..96d959427e 100644
--- a/include/openssl/ssl.h
+++ b/include/openssl/ssl.h
@@ -173,9 +173,15 @@ extern "C" {
# define SSL_DEFAULT_CIPHER_LIST "ALL:!COMPLEMENTOFDEFAULT:!eNULL"
/* This is the default set of TLSv1.3 ciphersuites */
# if !defined(OPENSSL_NO_CHACHA) && !defined(OPENSSL_NO_POLY1305)
-# define TLS_DEFAULT_CIPHERSUITES "TLS_AES_256_GCM_SHA384:" \
- "TLS_CHACHA20_POLY1305_SHA256:" \
- "TLS_AES_128_GCM_SHA256"
+# ifdef OPENSSL_PREFER_CHACHA_OVER_GCM
+# define TLS_DEFAULT_CIPHERSUITES "TLS_CHACHA20_POLY1305_SHA256:" \
+ "TLS_AES_256_GCM_SHA384:" \
+ "TLS_AES_128_GCM_SHA256"
+# else
+# define TLS_DEFAULT_CIPHERSUITES "TLS_AES_256_GCM_SHA384:" \
+ "TLS_CHACHA20_POLY1305_SHA256:" \
+ "TLS_AES_128_GCM_SHA256"
+# endif
# else
# define TLS_DEFAULT_CIPHERSUITES "TLS_AES_256_GCM_SHA384:" \
"TLS_AES_128_GCM_SHA256"
diff --git a/ssl/ssl_ciph.c b/ssl/ssl_ciph.c
index 27a1b2ec68..7039811323 100644
--- a/ssl/ssl_ciph.c
+++ b/ssl/ssl_ciph.c
@@ -1467,11 +1467,29 @@ STACK_OF(SSL_CIPHER) *ssl_create_cipher_list(const SSL_METHOD *ssl_method,
ssl_cipher_apply_rule(0, SSL_kECDHE, 0, 0, 0, 0, 0, CIPHER_DEL, -1, &head,
&tail);
+ /*
+ * If OPENSSL_PREFER_CHACHA_OVER_GCM is defined, ChaCha20_Poly1305
+ * will be placed before AES-256. Otherwise, the default behavior of
+ * preferring GCM over CHACHA is used.
+ * This is useful for systems that do not have AES-specific CPU
+ * instructions, where ChaCha20-Poly1305 is 3 times faster than AES.
+ * Note that this does not have the same effect as the SSL_OP_PRIORITIZE_CHACHA
+ * option, which prioritizes ChaCha20-Poly1305 only when the client has it on top
+ * of its ciphersuite preference.
+ */
+
+#ifdef OPENSSL_PREFER_CHACHA_OVER_GCM
+ ssl_cipher_apply_rule(0, 0, 0, SSL_CHACHA20, 0, 0, 0, CIPHER_ADD, -1,
+ &head, &tail);
+ ssl_cipher_apply_rule(0, 0, 0, SSL_AESGCM, 0, 0, 0, CIPHER_ADD, -1,
+ &head, &tail);
+#else
/* Within each strength group, we prefer GCM over CHACHA... */
ssl_cipher_apply_rule(0, 0, 0, SSL_AESGCM, 0, 0, 0, CIPHER_ADD, -1,
&head, &tail);
ssl_cipher_apply_rule(0, 0, 0, SSL_CHACHA20, 0, 0, 0, CIPHER_ADD, -1,
&head, &tail);
+#endif
/*
* ...and generally, our preferred cipher is AES.
@@ -1527,7 +1545,7 @@ STACK_OF(SSL_CIPHER) *ssl_create_cipher_list(const SSL_METHOD *ssl_method,
* Within each group, ciphers remain sorted by strength and previous
* preference, i.e.,
* 1) ECDHE > DHE
- * 2) GCM > CHACHA
+ * 2) GCM > CHACHA, reversed if OPENSSL_PREFER_CHACHA_OVER_GCM is defined
* 3) AES > rest
* 4) TLS 1.2 > legacy
*
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