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Diffstat (limited to 'src/tls/tls_dh.c')
-rw-r--r-- | src/tls/tls_dh.c | 387 |
1 files changed, 387 insertions, 0 deletions
diff --git a/src/tls/tls_dh.c b/src/tls/tls_dh.c new file mode 100644 index 0000000..70db8e9 --- /dev/null +++ b/src/tls/tls_dh.c @@ -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 |