Auto DH support.
Add auto DH parameter support. This is roughly equivalent to the
ECDH auto curve selection but for DH. An application can just call
SSL_CTX_set_auto_dh(ctx, 1);
and appropriate DH parameters will be used based on the size of the
server key.
Unlike ECDH there is no way a peer can indicate the range of DH parameters
it supports. Some peers cannot handle DH keys larger that 1024 bits for
example. In this case if you call:
SSL_CTX_set_auto_dh(ctx, 2);
Only 1024 bit DH parameters will be used.
If the server key is 7680 bits or more in size then 8192 bit DH parameters
will be used: these will be *very* slow.
The old export ciphersuites aren't supported but those are very
insecure anyway.
diff --git a/ssl/t1_lib.c b/ssl/t1_lib.c
index 31fc70e..c9e4898 100644
--- a/ssl/t1_lib.c
+++ b/ssl/t1_lib.c
@@ -115,6 +115,10 @@
#include <openssl/hmac.h>
#include <openssl/ocsp.h>
#include <openssl/rand.h>
+#ifndef OPENSSL_NO_DH
+#include <openssl/dh.h>
+#include <openssl/bn.h>
+#endif
#include "ssl_locl.h"
const char tls1_version_str[]="TLSv1" OPENSSL_VERSION_PTEXT;
@@ -4439,3 +4443,47 @@
}
#endif
+
+#ifndef OPENSSL_NO_DH
+DH *ssl_get_auto_dh(SSL *s)
+ {
+ int dh_secbits = 80;
+ if (s->cert->dh_tmp_auto == 2)
+ return DH_get_1024_160();
+ if (s->s3->tmp.new_cipher->algorithm_auth & SSL_aNULL)
+ {
+ if (s->s3->tmp.new_cipher->strength_bits == 256)
+ dh_secbits = 128;
+ else
+ dh_secbits = 80;
+ }
+ else
+ {
+ CERT_PKEY *cpk = ssl_get_server_send_pkey(s);
+ dh_secbits = EVP_PKEY_security_bits(cpk->privatekey);
+ }
+
+ if (dh_secbits >= 128)
+ {
+ DH *dhp = DH_new();
+ if (!dhp)
+ return NULL;
+ dhp->g = BN_new();
+ if (dhp->g)
+ BN_set_word(dhp->g, 2);
+ if (dh_secbits >= 192)
+ dhp->p = get_rfc3526_prime_8192(NULL);
+ else
+ dhp->p = get_rfc3526_prime_3072(NULL);
+ if (!dhp->p || !dhp->g)
+ {
+ DH_free(dhp);
+ return NULL;
+ }
+ return dhp;
+ }
+ if (dh_secbits >= 112)
+ return DH_get_2048_224();
+ return DH_get_1024_160();
+ }
+#endif
