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-rw-r--r--src/tls/tls_dh.c387
1 files changed, 387 insertions, 0 deletions
diff --git a/src/tls/tls_dh.c b/src/tls/tls_dh.c
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@@ -0,0 +1,387 @@
+/*++
+/* NAME
+/* tls_dh
+/* SUMMARY
+/* Diffie-Hellman parameter support
+/* SYNOPSIS
+/* #define TLS_INTERNAL
+/* #include <tls.h>
+/*
+/* void tls_set_dh_from_file(path, bits)
+/* const char *path;
+/* int bits;
+/*
+/* void tls_auto_eecdh_curves(ctx, configured)
+/* SSL_CTX *ctx;
+/* char *configured;
+/*
+/* void tls_set_eecdh_curve(server_ctx, grade)
+/* SSL_CTX *server_ctx;
+/* const char *grade;
+/*
+/* DH *tls_tmp_dh_cb(ssl, export, keylength)
+/* SSL *ssl; /* unused */
+/* int export;
+/* int keylength;
+/* DESCRIPTION
+/* This module maintains parameters for Diffie-Hellman key generation.
+/*
+/* tls_tmp_dh_cb() is a call-back routine for the
+/* SSL_CTX_set_tmp_dh_callback() function.
+/*
+/* tls_set_dh_from_file() overrides compiled-in DH parameters
+/* with those specified in the named files. The file format
+/* is as expected by the PEM_read_DHparams() routine. The
+/* "bits" argument must be 512 or 1024.
+/*
+/* tls_auto_eecdh_curves() enables negotiation of the most preferred curve
+/* among the curves specified by the "configured" argument.
+/*
+/* tls_set_eecdh_curve() enables ephemeral Elliptic-Curve DH
+/* key exchange algorithms by instantiating in the server SSL
+/* context a suitable curve (corresponding to the specified
+/* EECDH security grade) from the set of named curves in RFC
+/* 4492 Section 5.1.1. Errors generate warnings, but do not
+/* disable TLS, rather we continue without EECDH. A zero
+/* result indicates that the grade is invalid or the corresponding
+/* curve could not be used. The "auto" grade enables multiple
+/* curves, with the actual curve chosen as the most preferred
+/* among those supported by both the server and the client.
+/* DIAGNOSTICS
+/* In case of error, tls_set_dh_from_file() logs a warning and
+/* ignores the request.
+/* LICENSE
+/* .ad
+/* .fi
+/* This software is free. You can do with it whatever you want.
+/* The original author kindly requests that you acknowledge
+/* the use of his software.
+/* AUTHOR(S)
+/* Originally written by:
+/* Lutz Jaenicke
+/* BTU Cottbus
+/* Allgemeine Elektrotechnik
+/* Universitaetsplatz 3-4
+/* D-03044 Cottbus, Germany
+/*
+/* Updated by:
+/* Wietse Venema
+/* IBM T.J. Watson Research
+/* P.O. Box 704
+/* Yorktown Heights, NY 10598, USA
+/*--*/
+
+/* System library. */
+
+#include <sys_defs.h>
+
+#ifdef USE_TLS
+#include <stdio.h>
+
+/* Utility library. */
+
+#include <msg.h>
+#include <mymalloc.h>
+#include <stringops.h>
+
+ /*
+ * Global library
+ */
+#include <mail_params.h>
+
+/* TLS library. */
+
+#define TLS_INTERNAL
+#include <tls.h>
+#include <openssl/dh.h>
+#ifndef OPENSSL_NO_ECDH
+#include <openssl/ec.h>
+#endif
+
+/* Application-specific. */
+
+ /*
+ * Compiled-in DH parameters. Used when no parameters are explicitly loaded
+ * from a site-specific file. Using an ASN.1 DER encoding avoids the need
+ * to explicitly manipulate the internal representation of DH parameter
+ * objects.
+ *
+ * 512-bit parameters are used for export ciphers, and 2048-bit parameters are
+ * used for non-export ciphers. The non-export group is now 2048-bit, as
+ * 1024 bits is increasingly considered to weak by clients. When greater
+ * security is required, use EECDH.
+ */
+
+ /*-
+ * Generated via:
+ * $ openssl dhparam -2 -outform DER 512 2>/dev/null |
+ * hexdump -ve '/1 "0x%02x, "' | fmt
+ * TODO: generate at compile-time. But that is no good for the majority of
+ * sites that install pre-compiled binaries, and breaks reproducible builds.
+ * Instead, generate at installation time and use main.cf configuration.
+ */
+static unsigned char dh512_der[] = {
+ 0x30, 0x46, 0x02, 0x41, 0x00, 0xd8, 0xbf, 0x11, 0xd6, 0x41, 0x2a, 0x7a,
+ 0x9c, 0x78, 0xb2, 0xaa, 0x41, 0x23, 0x0a, 0xdc, 0xcf, 0xb7, 0x19, 0xc5,
+ 0x16, 0x4c, 0xcb, 0x4a, 0xd0, 0xd2, 0x1f, 0x1f, 0x70, 0x24, 0x86, 0x6f,
+ 0x51, 0x52, 0xc6, 0x5b, 0x28, 0xbb, 0x82, 0xe1, 0x24, 0x91, 0x3d, 0x4d,
+ 0x95, 0x56, 0xf8, 0x0b, 0x2c, 0xe0, 0x36, 0x67, 0x88, 0x64, 0x15, 0x1f,
+ 0x45, 0xd5, 0xb8, 0x0a, 0x00, 0x03, 0x76, 0x32, 0x0b, 0x02, 0x01, 0x02,
+};
+
+ /*-
+ * Generated via:
+ * $ openssl dhparam -2 -outform DER 2048 2>/dev/null |
+ * hexdump -ve '/1 "0x%02x, "' | fmt
+ * TODO: generate at compile-time. But that is no good for the majority of
+ * sites that install pre-compiled binaries, and breaks reproducible builds.
+ * Instead, generate at installation time and use main.cf configuration.
+ */
+static unsigned char dh2048_der[] = {
+ 0x30, 0x82, 0x01, 0x08, 0x02, 0x82, 0x01, 0x01, 0x00, 0xbf, 0x28, 0x1b,
+ 0x68, 0x69, 0x90, 0x2f, 0x37, 0x9f, 0x5a, 0x50, 0x23, 0x73, 0x2c, 0x11,
+ 0xf2, 0xac, 0x7c, 0x3e, 0x58, 0xb9, 0x23, 0x3e, 0x02, 0x07, 0x4d, 0xba,
+ 0xd9, 0x2c, 0xc1, 0x9e, 0xf9, 0xc4, 0x2f, 0xbc, 0x8d, 0x86, 0x4b, 0x2a,
+ 0x87, 0x86, 0x93, 0x32, 0x0f, 0x72, 0x40, 0xfe, 0x7e, 0xa2, 0xc1, 0x32,
+ 0xf0, 0x65, 0x9c, 0xc3, 0x19, 0x25, 0x2d, 0xeb, 0x6a, 0x49, 0x94, 0x79,
+ 0x2d, 0xa1, 0xbe, 0x05, 0x26, 0xac, 0x8d, 0x69, 0xdc, 0x2e, 0x7e, 0xb5,
+ 0xfd, 0x3c, 0x2b, 0x7d, 0x43, 0x22, 0x53, 0xf6, 0x1e, 0x04, 0x45, 0xd7,
+ 0x53, 0x84, 0xfd, 0x6b, 0x12, 0x72, 0x47, 0x04, 0xaf, 0xa4, 0xac, 0x4b,
+ 0x55, 0xb6, 0x79, 0x42, 0x40, 0x88, 0x54, 0x48, 0xd5, 0x4d, 0x3a, 0xb2,
+ 0xbf, 0x6c, 0x26, 0x95, 0x29, 0xdd, 0x8b, 0x9e, 0xed, 0xb8, 0x60, 0x8e,
+ 0xb5, 0x35, 0xb6, 0x22, 0x44, 0x1f, 0xfb, 0x56, 0x74, 0xfe, 0xf0, 0x2c,
+ 0xe6, 0x0c, 0x22, 0xc9, 0x35, 0xb3, 0x1b, 0x96, 0xbb, 0x0a, 0x5a, 0xc3,
+ 0x09, 0xa0, 0xcc, 0xa5, 0x40, 0x90, 0x0f, 0x59, 0xa2, 0x89, 0x69, 0x2a,
+ 0x69, 0x79, 0xe4, 0xd3, 0x24, 0xc6, 0x8c, 0xda, 0xbc, 0x98, 0x3a, 0x5b,
+ 0x16, 0xae, 0x63, 0x6c, 0x0b, 0x43, 0x4f, 0xf3, 0x2e, 0xc8, 0xa9, 0x6b,
+ 0x58, 0x6a, 0xa9, 0x8e, 0x64, 0x09, 0x3d, 0x88, 0x44, 0x4f, 0x97, 0x2c,
+ 0x1d, 0x98, 0xb0, 0xa9, 0xc0, 0xb6, 0x8d, 0x19, 0x37, 0x1f, 0xb7, 0xc9,
+ 0x86, 0xa8, 0xdc, 0x37, 0x4d, 0x64, 0x27, 0xf3, 0xf5, 0x2b, 0x7b, 0x6b,
+ 0x76, 0x84, 0x3f, 0xc1, 0x23, 0x97, 0x2d, 0x71, 0xf7, 0xb6, 0xc2, 0x35,
+ 0x28, 0x10, 0x96, 0xd6, 0x69, 0x0c, 0x2e, 0x1f, 0x9f, 0xdf, 0x82, 0x81,
+ 0x57, 0x57, 0x39, 0xa5, 0xf2, 0x81, 0x29, 0x57, 0xf9, 0x2f, 0xd0, 0x03,
+ 0xab, 0x02, 0x01, 0x02,
+};
+
+ /*
+ * Cached results.
+ */
+static DH *dh_1024 = 0;
+static DH *dh_512 = 0;
+
+/* tls_set_dh_from_file - set Diffie-Hellman parameters from file */
+
+void tls_set_dh_from_file(const char *path, int bits)
+{
+ FILE *paramfile;
+ DH **dhPtr;
+
+ switch (bits) {
+ case 512:
+ dhPtr = &dh_512;
+ break;
+ case 1024:
+ dhPtr = &dh_1024;
+ break;
+ default:
+ msg_panic("Invalid DH parameters size %d, file %s", bits, path);
+ }
+
+ /*
+ * This function is the first to set the DH parameters, but free any
+ * prior value just in case the call sequence changes some day.
+ */
+ if (*dhPtr) {
+ DH_free(*dhPtr);
+ *dhPtr = 0;
+ }
+ if ((paramfile = fopen(path, "r")) != 0) {
+ if ((*dhPtr = PEM_read_DHparams(paramfile, 0, 0, 0)) == 0) {
+ msg_warn("cannot load %d-bit DH parameters from file %s"
+ " -- using compiled-in defaults", bits, path);
+ tls_print_errors();
+ }
+ (void) fclose(paramfile); /* 200411 */
+ } else {
+ msg_warn("cannot load %d-bit DH parameters from file %s: %m"
+ " -- using compiled-in defaults", bits, path);
+ }
+}
+
+/* tls_get_dh - get compiled-in DH parameters */
+
+static DH *tls_get_dh(const unsigned char *p, size_t plen)
+{
+ const unsigned char *endp = p;
+ DH *dh = 0;
+
+ if (d2i_DHparams(&dh, &endp, plen) && plen == endp - p)
+ return (dh);
+
+ msg_warn("cannot load compiled-in DH parameters");
+ if (dh)
+ DH_free(dh);
+ return (0);
+}
+
+/* tls_tmp_dh_cb - call-back for Diffie-Hellman parameters */
+
+DH *tls_tmp_dh_cb(SSL *unused_ssl, int export, int keylength)
+{
+ DH *dh_tmp;
+
+ if (export && keylength == 512) { /* 40-bit export cipher */
+ if (dh_512 == 0)
+ dh_512 = tls_get_dh(dh512_der, sizeof(dh512_der));
+ dh_tmp = dh_512;
+ } else { /* ADH, DHE-RSA or DSA */
+ if (dh_1024 == 0)
+ dh_1024 = tls_get_dh(dh2048_der, sizeof(dh2048_der));
+ dh_tmp = dh_1024;
+ }
+ return (dh_tmp);
+}
+
+void tls_auto_eecdh_curves(SSL_CTX *ctx, const char *configured)
+{
+#ifndef OPENSSL_NO_ECDH
+ SSL_CTX *tmpctx;
+ int *nids;
+ int space = 5;
+ int n = 0;
+ int unknown = 0;
+ char *save;
+ char *curves;
+ char *curve;
+
+ if ((tmpctx = SSL_CTX_new(TLS_method())) == 0) {
+ msg_warn("cannot allocate temp SSL_CTX, using default ECDHE curves");
+ tls_print_errors();
+ return;
+ }
+ nids = mymalloc(space * sizeof(int));
+ curves = save = mystrdup(configured);
+#define RETURN do { \
+ myfree(save); \
+ myfree(nids); \
+ SSL_CTX_free(tmpctx); \
+ return; \
+ } while (0)
+
+ while ((curve = mystrtok(&curves, CHARS_COMMA_SP)) != 0) {
+ int nid = EC_curve_nist2nid(curve);
+
+ if (nid == NID_undef)
+ nid = OBJ_sn2nid(curve);
+ if (nid == NID_undef)
+ nid = OBJ_ln2nid(curve);
+ if (nid == NID_undef) {
+ msg_warn("ignoring unknown ECDHE curve \"%s\"",
+ curve);
+ continue;
+ }
+
+ /*
+ * Validate the NID by trying it as the sole EC curve for a
+ * throw-away SSL context. Silently skip unsupported code points.
+ * This way, we can list X25519 and X448 as soon as the nids are
+ * assigned, and before the supporting code is implemented. They'll
+ * be silently skipped when not yet supported.
+ */
+ if (SSL_CTX_set1_curves(tmpctx, &nid, 1) <= 0) {
+ ++unknown;
+ continue;
+ }
+ if (++n > space) {
+ space *= 2;
+ nids = myrealloc(nids, space * sizeof(int));
+ }
+ nids[n - 1] = nid;
+ }
+
+ if (n == 0) {
+ if (unknown > 0)
+ msg_warn("none of the configured ECDHE curves are supported");
+ RETURN;
+ }
+ if (SSL_CTX_set1_curves(ctx, nids, n) <= 0) {
+ msg_warn("failed to configure ECDHE curves");
+ tls_print_errors();
+ RETURN;
+ }
+
+ /*
+ * This is a NOP in OpenSSL 1.1.0 and later, where curves are always
+ * auto-negotiated.
+ */
+#if OPENSSL_VERSION_NUMBER < 0x10100000UL
+ if (SSL_CTX_set_ecdh_auto(ctx, 1) <= 0) {
+ msg_warn("failed to enable automatic ECDHE curve selection");
+ tls_print_errors();
+ RETURN;
+ }
+#endif
+ RETURN;
+#endif
+}
+
+#define TLS_EECDH_INVALID 0
+#define TLS_EECDH_NONE 1
+#define TLS_EECDH_STRONG 2
+#define TLS_EECDH_ULTRA 3
+#define TLS_EECDH_AUTO 4
+
+void tls_set_eecdh_curve(SSL_CTX *server_ctx, const char *grade)
+{
+#ifndef OPENSSL_NO_ECDH
+ int g;
+ static NAME_CODE eecdh_table[] = {
+ "none", TLS_EECDH_NONE,
+ "strong", TLS_EECDH_STRONG,
+ "ultra", TLS_EECDH_ULTRA,
+ "auto", TLS_EECDH_AUTO,
+ 0, TLS_EECDH_INVALID,
+ };
+
+ switch (g = name_code(eecdh_table, NAME_CODE_FLAG_NONE, grade)) {
+ default:
+ msg_panic("Invalid eecdh grade code: %d", g);
+ case TLS_EECDH_INVALID:
+ msg_warn("Invalid TLS eecdh grade \"%s\": EECDH disabled", grade);
+ return;
+ case TLS_EECDH_STRONG:
+ tls_auto_eecdh_curves(server_ctx, var_tls_eecdh_strong);
+ return;
+ case TLS_EECDH_ULTRA:
+ tls_auto_eecdh_curves(server_ctx, var_tls_eecdh_ultra);
+ return;
+ case TLS_EECDH_NONE:
+
+ /*
+ * Pretend "none" is "auto", the former is no longer supported or
+ * wise
+ */
+ msg_warn("The \"none\" eecdh grade is no longer supported, "
+ "using \"auto\" instead");
+ case TLS_EECDH_AUTO:
+ tls_auto_eecdh_curves(server_ctx, var_tls_eecdh_auto);
+ return;
+ }
+#endif
+ return;
+}
+
+#ifdef TEST
+
+int main(int unused_argc, char **unused_argv)
+{
+ tls_tmp_dh_cb(0, 1, 512);
+ tls_tmp_dh_cb(0, 1, 1024);
+ tls_tmp_dh_cb(0, 1, 2048);
+ tls_tmp_dh_cb(0, 0, 512);
+ return (0);
+}
+
+#endif
+
+#endif
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