Optionally, retain only SHA-256 of client cert.

Adds an option to retain only the SHA256 of a client certificate in
memory and in the serialized session state.

ssl/s3_srvr.c

@@ -756,6 +756,14 @@ int ssl3_accept(SSL *s)
 
 			s->init_num=0;
 
+			/* If we aren't retaining peer certificates then we can
+			 * discard it now. */
+			if (s->session->peer && s->ctx->retain_only_sha256_of_client_certs)
+				{
+				X509_free(s->session->peer);
+				s->session->peer = NULL;
+				}
+
 			if (s->renegotiate == 2) /* skipped if we just sent a HelloRequest */
 				{
 				s->renegotiate=0;
@@ -2811,6 +2819,7 @@ int ssl3_get_client_certificate(SSL *s)
 	const unsigned char *p,*q;
 	unsigned char *d;
 	STACK_OF(X509) *sk=NULL;
+	SHA256_CTX sha256;
 
 	n=s->method->ssl_get_message(s,
 		SSL3_ST_SR_CERT_A,
@@ -2872,6 +2881,17 @@ int ssl3_get_client_certificate(SSL *s)
 			goto f_err;
 			}
 
+		if (nc == 0 && s->ctx->retain_only_sha256_of_client_certs)
+			{
+			/* If this is the first certificate, and we don't want
+			 * to keep peer certificates in memory, then we hash it
+			 * right away. */
+			SHA256_Init(&sha256);
+			SHA256_Update(&sha256, p, l);
+			SHA256_Final(s->session->peer_sha256, &sha256);
+			s->session->peer_sha256_valid = 1;
+			}
+
 		q=p;
 		x=d2i_X509(NULL,&p,l);
 		if (x == NULL)

ssl/ssl.h

@@ -501,6 +501,7 @@ struct ssl_method_st
  *	Ticket [10]             EXPLICIT OCTET STRING, -- session ticket (clients only)
  *	Compression_meth [11]   EXPLICIT OCTET STRING, -- optional compression method
  *	SRP_username [ 12 ] EXPLICIT OCTET STRING -- optional SRP username
+ *	Peer SHA256 [13]        EXPLICIT OCTET STRING, -- optional SHA256 hash of Peer certifiate
  *	}
  * Look in ssl/ssl_asn1.c for more details
  * I'm using EXPLICIT tags so I can read the damn things using asn1parse :-).
@@ -576,6 +577,8 @@ struct ssl_session_st
 	size_t tlsext_ticklen;		/* Session ticket length */
 	long tlsext_tick_lifetime_hint;	/* Session lifetime hint in seconds */
 #endif
+	char peer_sha256_valid;		/* Non-zero if peer_sha256 is valid */
+	unsigned char peer_sha256[SHA256_DIGEST_LENGTH];  /* SHA256 of peer certificate */
 #ifndef OPENSSL_NO_TLSEXT
 	/* Used by client: the proof for this session.
 	 * We store it outside the sess_cert structure, since the proof
@@ -1034,6 +1037,10 @@ struct ssl_ctx_st
 	unsigned int freelist_max_len;
 	struct ssl3_buf_freelist_st *wbuf_freelist;
 	struct ssl3_buf_freelist_st *rbuf_freelist;
+	/* retain_only_sha256_of_client_certs is true if we should compute the
+	 * SHA256 hash of the peer's certifiate and then discard it to save
+	 * memory and session space. Only effective on the server side. */
+	char retain_only_sha256_of_client_certs;
 #endif
 
 #ifndef OPENSSL_NO_TLSEXT

ssl/ssl_asn1.c

@@ -121,12 +121,13 @@ typedef struct ssl_session_asn1_st
 	ASN1_OCTET_STRING psk_identity_hint;
 	ASN1_OCTET_STRING psk_identity;
 #endif /* OPENSSL_NO_PSK */
+	ASN1_OCTET_STRING peer_sha256;
 	} SSL_SESSION_ASN1;
 
 int i2d_SSL_SESSION(SSL_SESSION *in, unsigned char **pp)
 	{
 #define LSIZE2 (sizeof(long)*2)
-	int v1=0,v2=0,v3=0,v4=0,v5=0,v7=0,v8=0;
+	int v1=0,v2=0,v3=0,v4=0,v5=0,v7=0,v8=0,v13=0;
 	unsigned char buf[4],ibuf1[LSIZE2],ibuf2[LSIZE2];
 	unsigned char ibuf3[LSIZE2],ibuf4[LSIZE2],ibuf5[LSIZE2];
 #ifndef OPENSSL_NO_TLSEXT
@@ -251,6 +252,13 @@ int i2d_SSL_SESSION(SSL_SESSION *in, unsigned char **pp)
 		a.psk_identity.type=V_ASN1_OCTET_STRING;
 		a.psk_identity.data=(unsigned char *)(in->psk_identity);
 		}
+
+	if (in->peer_sha256_valid)
+		{
+		a.peer_sha256.length = sizeof(in->peer_sha256);
+		a.peer_sha256.type = V_ASN1_OCTET_STRING;
+		a.peer_sha256.data = in->peer_sha256;
+		}
 #endif /* OPENSSL_NO_PSK */
 
 	M_ASN1_I2D_len(&(a.version),		i2d_ASN1_INTEGER);
@@ -264,7 +272,7 @@ int i2d_SSL_SESSION(SSL_SESSION *in, unsigned char **pp)
 		M_ASN1_I2D_len_EXP_opt(&(a.time),i2d_ASN1_INTEGER,1,v1);
 	if (in->timeout != 0L)
 		M_ASN1_I2D_len_EXP_opt(&(a.timeout),i2d_ASN1_INTEGER,2,v2);
-	if (in->peer != NULL)
+	if (in->peer != NULL && in->peer_sha256_valid == 0)
 		M_ASN1_I2D_len_EXP_opt(in->peer,i2d_X509,3,v3);
 	M_ASN1_I2D_len_EXP_opt(&a.session_id_context,i2d_ASN1_OCTET_STRING,4,v4);
 	if (in->verify_result != X509_V_OK)
@@ -284,6 +292,8 @@ int i2d_SSL_SESSION(SSL_SESSION *in, unsigned char **pp)
 	if (in->psk_identity)
         	M_ASN1_I2D_len_EXP_opt(&(a.psk_identity), i2d_ASN1_OCTET_STRING,8,v8);
 #endif /* OPENSSL_NO_PSK */
+	if (in->peer_sha256_valid)
+		M_ASN1_I2D_len_EXP_opt(&(a.peer_sha256),i2d_ASN1_OCTET_STRING,13,v13);
 
 	M_ASN1_I2D_seq_total();
 
@@ -298,7 +308,7 @@ int i2d_SSL_SESSION(SSL_SESSION *in, unsigned char **pp)
 		M_ASN1_I2D_put_EXP_opt(&(a.time),i2d_ASN1_INTEGER,1,v1);
 	if (in->timeout != 0L)
 		M_ASN1_I2D_put_EXP_opt(&(a.timeout),i2d_ASN1_INTEGER,2,v2);
-	if (in->peer != NULL)
+	if (in->peer != NULL && in->peer_sha256_valid == 0)
 		M_ASN1_I2D_put_EXP_opt(in->peer,i2d_X509,3,v3);
 	M_ASN1_I2D_put_EXP_opt(&a.session_id_context,i2d_ASN1_OCTET_STRING,4,
 			       v4);
@@ -320,6 +330,8 @@ int i2d_SSL_SESSION(SSL_SESSION *in, unsigned char **pp)
 	if (in->tlsext_tick)
         	M_ASN1_I2D_put_EXP_opt(&(a.tlsext_tick), i2d_ASN1_OCTET_STRING,10,v10);
 #endif /* OPENSSL_NO_TLSEXT */
+	if (in->peer_sha256_valid)
+		M_ASN1_I2D_put_EXP_opt(&(a.peer_sha256),i2d_ASN1_OCTET_STRING,13,v13);
 	M_ASN1_I2D_finish();
 	}
 
@@ -541,5 +553,16 @@ SSL_SESSION *d2i_SSL_SESSION(SSL_SESSION **a, const unsigned char **pp,
 		ret->tlsext_tick=NULL;
 #endif /* OPENSSL_NO_TLSEXT */
 
+	os.length=0;
+	os.data=NULL;
+	M_ASN1_D2I_get_EXP_opt(osp,d2i_ASN1_OCTET_STRING,13);
+	if (os.data && os.length == sizeof(ret->peer_sha256))
+		{
+		memcpy(ret->peer_sha256, os.data, sizeof(ret->peer_sha256));
+		ret->peer_sha256_valid = 1;
+		OPENSSL_free(os.data);
+		os.data = NULL;
+		}
+
 	M_ASN1_D2I_Finish(a,SSL_SESSION_free,SSL_F_D2I_SSL_SESSION);
 	}