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tor/src/common/crypto_ed25519.c

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/* Copyright (c) 2013-2016, The Tor Project, Inc. */
/* See LICENSE for licensing information */
/**
* \file crypto_ed25519.c
*
* \brief Wrapper code for an ed25519 implementation.
*
* Ed25519 is a Schnorr signature on a Twisted Edwards curve, defined
* by Dan Bernstein. For more information, see https://ed25519.cr.yp.to/
*
* This module wraps our choice of Ed25519 backend, and provides a few
* convenience functions for checking and generating signatures. It also
* provides Tor-specific tools for key blinding and for converting Ed25519
* keys to and from the corresponding Curve25519 keys.
*/
#include "orconfig.h"
#ifdef HAVE_SYS_STAT_H
#include <sys/stat.h>
#endif
#include "crypto.h"
#include "crypto_curve25519.h"
#include "crypto_ed25519.h"
#include "crypto_format.h"
#include "torlog.h"
#include "util.h"
#include "ed25519/ref10/ed25519_ref10.h"
#include "ed25519/donna/ed25519_donna_tor.h"
#include <openssl/sha.h>
static void pick_ed25519_impl(void);
static int ed25519_impl_spot_check(void);
/** An Ed25519 implementation, as a set of function pointers. */
typedef struct {
int (*selftest)(void);
int (*seckey)(unsigned char *);
int (*seckey_expand)(unsigned char *, const unsigned char *);
int (*pubkey)(unsigned char *, const unsigned char *);
int (*keygen)(unsigned char *, unsigned char *);
int (*open)(const unsigned char *, const unsigned char *, size_t, const
unsigned char *);
int (*sign)(unsigned char *, const unsigned char *, size_t,
const unsigned char *, const unsigned char *);
int (*open_batch)(const unsigned char **, size_t *, const unsigned char **,
const unsigned char **, size_t, int *);
int (*blind_secret_key)(unsigned char *, const unsigned char *,
const unsigned char *);
int (*blind_public_key)(unsigned char *, const unsigned char *,
const unsigned char *);
int (*pubkey_from_curve25519_pubkey)(unsigned char *, const unsigned char *,
int);
} ed25519_impl_t;
/** The Ref10 Ed25519 implementation. This one is pure C and lightly
* optimized. */
static const ed25519_impl_t impl_ref10 = {
NULL,
ed25519_ref10_seckey,
ed25519_ref10_seckey_expand,
ed25519_ref10_pubkey,
ed25519_ref10_keygen,
ed25519_ref10_open,
ed25519_ref10_sign,
NULL,
ed25519_ref10_blind_secret_key,
ed25519_ref10_blind_public_key,
ed25519_ref10_pubkey_from_curve25519_pubkey,
};
/** The Ref10 Ed25519 implementation. This one is heavily optimized, but still
* mostly C. The C still tends to be heavily platform-specific. */
static const ed25519_impl_t impl_donna = {
ed25519_donna_selftest,
ed25519_donna_seckey,
ed25519_donna_seckey_expand,
ed25519_donna_pubkey,
ed25519_donna_keygen,
ed25519_donna_open,
ed25519_donna_sign,
ed25519_sign_open_batch_donna,
ed25519_donna_blind_secret_key,
ed25519_donna_blind_public_key,
ed25519_donna_pubkey_from_curve25519_pubkey,
};
/** Which Ed25519 implementation are we using? NULL if we haven't decided
* yet. */
static const ed25519_impl_t *ed25519_impl = NULL;
/** Helper: Return our chosen Ed25519 implementation.
*
* This should only be called after we've picked an implementation, but
* it _does_ recover if you forget this.
**/
static inline const ed25519_impl_t *
get_ed_impl(void)
{
if (BUG(ed25519_impl == NULL)) {
pick_ed25519_impl(); // LCOV_EXCL_LINE - We always call ed25519_init().
}
return ed25519_impl;
}
#ifdef TOR_UNIT_TESTS
/** For testing: used to remember our actual choice of Ed25519
* implementation */
static const ed25519_impl_t *saved_ed25519_impl = NULL;
/** For testing: Use the Ed25519 implementation called <b>name</b> until
* crypto_ed25519_testing_restore_impl is called. Recognized names are
* "donna" and "ref10". */
void
crypto_ed25519_testing_force_impl(const char *name)
{
tor_assert(saved_ed25519_impl == NULL);
saved_ed25519_impl = ed25519_impl;
if (! strcmp(name, "donna")) {
ed25519_impl = &impl_donna;
} else {
tor_assert(!strcmp(name, "ref10"));
ed25519_impl = &impl_ref10;
}
}
/** For testing: go back to whatever Ed25519 implementation we had picked
* before crypto_ed25519_testing_force_impl was called.
*/
void
crypto_ed25519_testing_restore_impl(void)
{
ed25519_impl = saved_ed25519_impl;
saved_ed25519_impl = NULL;
}
#endif
/**
* Initialize a new ed25519 secret key in <b>seckey_out</b>. If
* <b>extra_strong</b>, take the RNG inputs directly from the operating
* system. Return 0 on success, -1 on failure.
*/
int
ed25519_secret_key_generate(ed25519_secret_key_t *seckey_out,
int extra_strong)
{
int r;
uint8_t seed[32];
if (extra_strong)
crypto_strongest_rand(seed, sizeof(seed));
else
crypto_rand((char*)seed, sizeof(seed));
r = get_ed_impl()->seckey_expand(seckey_out->seckey, seed);
memwipe(seed, 0, sizeof(seed));
return r < 0 ? -1 : 0;
}
/**
* Given a 32-byte random seed in <b>seed</b>, expand it into an ed25519
* secret key in <b>seckey_out</b>. Return 0 on success, -1 on failure.
*/
int
ed25519_secret_key_from_seed(ed25519_secret_key_t *seckey_out,
const uint8_t *seed)
{
if (get_ed_impl()->seckey_expand(seckey_out->seckey, seed) < 0)
return -1;
return 0;
}
/**
* Given a secret key in <b>seckey</b>, expand it into an
* ed25519 public key. Return 0 on success, -1 on failure.
*/
int
ed25519_public_key_generate(ed25519_public_key_t *pubkey_out,
const ed25519_secret_key_t *seckey)
{
if (get_ed_impl()->pubkey(pubkey_out->pubkey, seckey->seckey) < 0)
return -1;
return 0;
}
/** Generate a new ed25519 keypair in <b>keypair_out</b>. If
* <b>extra_strong</b> is set, try to mix some system entropy into the key
* generation process. Return 0 on success, -1 on failure. */
int
ed25519_keypair_generate(ed25519_keypair_t *keypair_out, int extra_strong)
{
if (ed25519_secret_key_generate(&keypair_out->seckey, extra_strong) < 0)
return -1;
if (ed25519_public_key_generate(&keypair_out->pubkey,
&keypair_out->seckey)<0)
return -1;
return 0;
}
/* Return a heap-allocated array that contains <b>msg</b> prefixed by the
* string <b>prefix_str</b>. Set <b>final_msg_len_out</b> to the size of the
* final array. If an error occured, return NULL. It's the resonsibility of the
* caller to free the returned array. */
static uint8_t *
get_prefixed_msg(const uint8_t *msg, size_t msg_len,
const char *prefix_str,
size_t *final_msg_len_out)
{
size_t prefixed_msg_len, prefix_len;
uint8_t *prefixed_msg;
tor_assert(prefix_str);
tor_assert(final_msg_len_out);
prefix_len = strlen(prefix_str);
/* msg_len + strlen(prefix_str) must not overflow. */
if (msg_len > SIZE_T_CEILING - prefix_len) {
return NULL;
}
prefixed_msg_len = msg_len + prefix_len;
prefixed_msg = tor_malloc_zero(prefixed_msg_len);
memcpy(prefixed_msg, prefix_str, prefix_len);
memcpy(prefixed_msg + prefix_len, msg, msg_len);
*final_msg_len_out = prefixed_msg_len;
return prefixed_msg;
}
/**
* Set <b>signature_out</b> to a signature of the <b>len</b>-byte message
* <b>msg</b>, using the secret and public key in <b>keypair</b>.
*
* Return 0 if we successfuly signed the message, otherwise return -1.
*/
int
ed25519_sign(ed25519_signature_t *signature_out,
const uint8_t *msg, size_t len,
const ed25519_keypair_t *keypair)
{
if (get_ed_impl()->sign(signature_out->sig, msg, len,
keypair->seckey.seckey,
keypair->pubkey.pubkey) < 0) {
return -1;
}
return 0;
}
/**
* Like ed25519_sign(), but also prefix <b>msg</b> with <b>prefix_str</b>
* before signing. <b>prefix_str</b> must be a NUL-terminated string.
*/
int
ed25519_sign_prefixed(ed25519_signature_t *signature_out,
const uint8_t *msg, size_t msg_len,
const char *prefix_str,
const ed25519_keypair_t *keypair)
{
int retval;
size_t prefixed_msg_len;
uint8_t *prefixed_msg;
tor_assert(prefix_str);
prefixed_msg = get_prefixed_msg(msg, msg_len, prefix_str,
&prefixed_msg_len);
if (!prefixed_msg) {
log_warn(LD_GENERAL, "Failed to get prefixed msg.");
return -1;
}
retval = ed25519_sign(signature_out,
prefixed_msg, prefixed_msg_len,
keypair);
tor_free(prefixed_msg);
return retval;
}
/**
* Check whether if <b>signature</b> is a valid signature for the
* <b>len</b>-byte message in <b>msg</b> made with the key <b>pubkey</b>.
*
* Return 0 if the signature is valid; -1 if it isn't.
*/
int
ed25519_checksig(const ed25519_signature_t *signature,
const uint8_t *msg, size_t len,
const ed25519_public_key_t *pubkey)
{
return
get_ed_impl()->open(signature->sig, msg, len, pubkey->pubkey) < 0 ? -1 : 0;
}
/**
* Like ed2519_checksig(), but also prefix <b>msg</b> with <b>prefix_str</b>
* before verifying signature. <b>prefix_str</b> must be a NUL-terminated
* string.
*/
int
ed25519_checksig_prefixed(const ed25519_signature_t *signature,
const uint8_t *msg, size_t msg_len,
const char *prefix_str,
const ed25519_public_key_t *pubkey)
{
int retval;
size_t prefixed_msg_len;
uint8_t *prefixed_msg;
prefixed_msg = get_prefixed_msg(msg, msg_len, prefix_str,
&prefixed_msg_len);
if (!prefixed_msg) {
log_warn(LD_GENERAL, "Failed to get prefixed msg.");
return -1;
}
retval = ed25519_checksig(signature,
prefixed_msg, prefixed_msg_len,
pubkey);
tor_free(prefixed_msg);
return retval;
}
/** Validate every signature among those in <b>checkable</b>, which contains
* exactly <b>n_checkable</b> elements. If <b>okay_out</b> is non-NULL, set
* the i'th element of <b>okay_out</b> to 1 if the i'th element of
* <b>checkable</b> is valid, and to 0 otherwise. Return 0 if every signature
* was valid. Otherwise return -N, where N is the number of invalid
* signatures.
*/
int
ed25519_checksig_batch(int *okay_out,
const ed25519_checkable_t *checkable,
int n_checkable)
{
int i, res;
const ed25519_impl_t *impl = get_ed_impl();
if (impl->open_batch == NULL) {
/* No batch verification implementation available, fake it by checking the
* each signature individually.
*/
res = 0;
for (i = 0; i < n_checkable; ++i) {
const ed25519_checkable_t *ch = &checkable[i];
int r = ed25519_checksig(&ch->signature, ch->msg, ch->len, ch->pubkey);
if (r < 0)
--res;
if (okay_out)
okay_out[i] = (r == 0);
}
} else {
/* ed25519-donna style batch verification available.
*
* Theoretically, this should only be called if n_checkable >= 3, since
* that's the threshold where the batch verification actually kicks in,
* but the only difference is a few mallocs/frees.
*/
const uint8_t **ms;
size_t *lens;
const uint8_t **pks;
const uint8_t **sigs;
int *oks;
int all_ok;
ms = tor_calloc(n_checkable, sizeof(uint8_t*));
lens = tor_calloc(n_checkable, sizeof(size_t));
pks = tor_calloc(n_checkable, sizeof(uint8_t*));
sigs = tor_calloc(n_checkable, sizeof(uint8_t*));
oks = okay_out ? okay_out : tor_calloc(n_checkable, sizeof(int));
for (i = 0; i < n_checkable; ++i) {
ms[i] = checkable[i].msg;
lens[i] = checkable[i].len;
pks[i] = checkable[i].pubkey->pubkey;
sigs[i] = checkable[i].signature.sig;
oks[i] = 0;
}
res = 0;
all_ok = impl->open_batch(ms, lens, pks, sigs, n_checkable, oks);
for (i = 0; i < n_checkable; ++i) {
if (!oks[i])
--res;
}
/* XXX: For now sanity check oks with the return value. Once we have
* more confidence in the code, if `all_ok == 0` we can skip iterating
* over oks since all the signatures were found to be valid.
*/
tor_assert(((res == 0) && !all_ok) || ((res < 0) && all_ok));
tor_free(ms);
tor_free(lens);
tor_free(pks);
tor_free(sigs);
if (! okay_out)
tor_free(oks);
}
return res;
}
/**
* Given a curve25519 keypair in <b>inp</b>, generate a corresponding
* ed25519 keypair in <b>out</b>, and set <b>signbit_out</b> to the
* sign bit of the X coordinate of the ed25519 key.
*
* NOTE THAT IT IS PROBABLY NOT SAFE TO USE THE GENERATED KEY FOR ANYTHING
* OUTSIDE OF WHAT'S PRESENTED IN PROPOSAL 228. In particular, it's probably
* not a great idea to use it to sign attacker-supplied anything.
*/
int
ed25519_keypair_from_curve25519_keypair(ed25519_keypair_t *out,
int *signbit_out,
const curve25519_keypair_t *inp)
{
const char string[] = "Derive high part of ed25519 key from curve25519 key";
ed25519_public_key_t pubkey_check;
SHA512_CTX ctx;
uint8_t sha512_output[64];
memcpy(out->seckey.seckey, inp->seckey.secret_key, 32);
SHA512_Init(&ctx);
SHA512_Update(&ctx, out->seckey.seckey, 32);
SHA512_Update(&ctx, string, sizeof(string));
SHA512_Final(sha512_output, &ctx);
memcpy(out->seckey.seckey + 32, sha512_output, 32);
ed25519_public_key_generate(&out->pubkey, &out->seckey);
*signbit_out = out->pubkey.pubkey[31] >> 7;
ed25519_public_key_from_curve25519_public_key(&pubkey_check, &inp->pubkey,
*signbit_out);
tor_assert(fast_memeq(pubkey_check.pubkey, out->pubkey.pubkey, 32));
memwipe(&pubkey_check, 0, sizeof(pubkey_check));
memwipe(&ctx, 0, sizeof(ctx));
memwipe(sha512_output, 0, sizeof(sha512_output));
return 0;
}
/**
* Given a curve25519 public key and sign bit of X coordinate of the ed25519
* public key, generate the corresponding ed25519 public key.
*/
int
ed25519_public_key_from_curve25519_public_key(ed25519_public_key_t *pubkey,
const curve25519_public_key_t *pubkey_in,
int signbit)
{
return get_ed_impl()->pubkey_from_curve25519_pubkey(pubkey->pubkey,
pubkey_in->public_key,
signbit);
}
/**
* Given an ed25519 keypair in <b>inp</b>, generate a corresponding
* ed25519 keypair in <b>out</b>, blinded by the corresponding 32-byte input
* in 'param'.
*
* Tor uses key blinding for the "next-generation" hidden services design:
* service descriptors are encrypted with a key derived from the service's
* long-term public key, and then signed with (and stored at a position
* indexed by) a short-term key derived by blinding the long-term keys.
*/
int
ed25519_keypair_blind(ed25519_keypair_t *out,
const ed25519_keypair_t *inp,
const uint8_t *param)
{
ed25519_public_key_t pubkey_check;
get_ed_impl()->blind_secret_key(out->seckey.seckey,
inp->seckey.seckey, param);
ed25519_public_blind(&pubkey_check, &inp->pubkey, param);
ed25519_public_key_generate(&out->pubkey, &out->seckey);
tor_assert(fast_memeq(pubkey_check.pubkey, out->pubkey.pubkey, 32));
memwipe(&pubkey_check, 0, sizeof(pubkey_check));
return 0;
}
/**
* Given an ed25519 public key in <b>inp</b>, generate a corresponding blinded
* public key in <b>out</b>, blinded with the 32-byte parameter in
* <b>param</b>. Return 0 on sucess, -1 on railure.
*/
int
ed25519_public_blind(ed25519_public_key_t *out,
const ed25519_public_key_t *inp,
const uint8_t *param)
{
get_ed_impl()->blind_public_key(out->pubkey, inp->pubkey, param);
return 0;
}
/**
* Store seckey unencrypted to <b>filename</b>, marking it with <b>tag</b>.
* Return 0 on success, -1 on failure.
*/
int
ed25519_seckey_write_to_file(const ed25519_secret_key_t *seckey,
const char *filename,
const char *tag)
{
return crypto_write_tagged_contents_to_file(filename,
"ed25519v1-secret",
tag,
seckey->seckey,
sizeof(seckey->seckey));
}
/**
* Read seckey unencrypted from <b>filename</b>, storing it into
* <b>seckey_out</b>. Set *<b>tag_out</b> to the tag it was marked with.
* Return 0 on success, -1 on failure.
*/
int
ed25519_seckey_read_from_file(ed25519_secret_key_t *seckey_out,
char **tag_out,
const char *filename)
{
ssize_t len;
len = crypto_read_tagged_contents_from_file(filename, "ed25519v1-secret",
tag_out, seckey_out->seckey,
sizeof(seckey_out->seckey));
if (len == sizeof(seckey_out->seckey)) {
return 0;
} else if (len >= 0) {
errno = EINVAL;
}
tor_free(*tag_out);
return -1;
}
/**
* Store pubkey unencrypted to <b>filename</b>, marking it with <b>tag</b>.
* Return 0 on success, -1 on failure.
*/
int
ed25519_pubkey_write_to_file(const ed25519_public_key_t *pubkey,
const char *filename,
const char *tag)
{
return crypto_write_tagged_contents_to_file(filename,
"ed25519v1-public",
tag,
pubkey->pubkey,
sizeof(pubkey->pubkey));
}
/**
* Store pubkey unencrypted to <b>filename</b>, marking it with <b>tag</b>.
* Return 0 on success, -1 on failure.
*/
int
ed25519_pubkey_read_from_file(ed25519_public_key_t *pubkey_out,
char **tag_out,
const char *filename)
{
ssize_t len;
len = crypto_read_tagged_contents_from_file(filename, "ed25519v1-public",
tag_out, pubkey_out->pubkey,
sizeof(pubkey_out->pubkey));
if (len == sizeof(pubkey_out->pubkey)) {
return 0;
} else if (len >= 0) {
errno = EINVAL;
}
tor_free(*tag_out);
return -1;
}
/** Release all storage held for <b>kp</b>. */
void
ed25519_keypair_free(ed25519_keypair_t *kp)
{
if (! kp)
return;
memwipe(kp, 0, sizeof(*kp));
tor_free(kp);
}
/** Return true iff <b>key1</b> and <b>key2</b> are the same public key. */
int
ed25519_pubkey_eq(const ed25519_public_key_t *key1,
const ed25519_public_key_t *key2)
{
tor_assert(key1);
tor_assert(key2);
return tor_memeq(key1->pubkey, key2->pubkey, ED25519_PUBKEY_LEN);
}
/** Check whether the given Ed25519 implementation seems to be working.
* If so, return 0; otherwise return -1. */
static int
ed25519_impl_spot_check(void)
{
static const uint8_t alicesk[32] = {
0xc5,0xaa,0x8d,0xf4,0x3f,0x9f,0x83,0x7b,
0xed,0xb7,0x44,0x2f,0x31,0xdc,0xb7,0xb1,
0x66,0xd3,0x85,0x35,0x07,0x6f,0x09,0x4b,
0x85,0xce,0x3a,0x2e,0x0b,0x44,0x58,0xf7
};
static const uint8_t alicepk[32] = {
0xfc,0x51,0xcd,0x8e,0x62,0x18,0xa1,0xa3,
0x8d,0xa4,0x7e,0xd0,0x02,0x30,0xf0,0x58,
0x08,0x16,0xed,0x13,0xba,0x33,0x03,0xac,
0x5d,0xeb,0x91,0x15,0x48,0x90,0x80,0x25
};
static const uint8_t alicemsg[2] = { 0xaf, 0x82 };
static const uint8_t alicesig[64] = {
0x62,0x91,0xd6,0x57,0xde,0xec,0x24,0x02,
0x48,0x27,0xe6,0x9c,0x3a,0xbe,0x01,0xa3,
0x0c,0xe5,0x48,0xa2,0x84,0x74,0x3a,0x44,
0x5e,0x36,0x80,0xd7,0xdb,0x5a,0xc3,0xac,
0x18,0xff,0x9b,0x53,0x8d,0x16,0xf2,0x90,
0xae,0x67,0xf7,0x60,0x98,0x4d,0xc6,0x59,
0x4a,0x7c,0x15,0xe9,0x71,0x6e,0xd2,0x8d,
0xc0,0x27,0xbe,0xce,0xea,0x1e,0xc4,0x0a
};
const ed25519_impl_t *impl = get_ed_impl();
uint8_t sk[ED25519_SECKEY_LEN];
uint8_t pk[ED25519_PUBKEY_LEN];
uint8_t sig[ED25519_SIG_LEN];
int r = 0;
/* Some implementations (eg: The modified Ed25519-donna) have handy self-test
* code that sanity-checks the internals. If present, use that to screen out
* catastrophic errors like massive compiler failure.
*/
if (impl->selftest && impl->selftest() != 0)
goto fail;
/* Validate results versus known answer tests. People really should be
* running "make test" instead of relying on this, but it's better than
* nothing.
*
* Test vectors taken from "EdDSA & Ed25519 - 6. Test Vectors for Ed25519
* (TEST3)" (draft-josefsson-eddsa-ed25519-03).
*/
/* Key expansion, public key derivation. */
if (impl->seckey_expand(sk, alicesk) < 0)
goto fail;
if (impl->pubkey(pk, sk) < 0)
goto fail;
if (fast_memneq(pk, alicepk, ED25519_PUBKEY_LEN))
goto fail;
/* Signing, verification. */
if (impl->sign(sig, alicemsg, sizeof(alicemsg), sk, pk) < 0)
return -1;
if (fast_memneq(sig, alicesig, ED25519_SIG_LEN))
return -1;
if (impl->open(sig, alicemsg, sizeof(alicemsg), pk) < 0)
return -1;
/* XXX/yawning: Someone that's more paranoid than I am, can write "Assume
* ref0 is cannonical, and fuzz impl against it" if they want, but I doubt
* that will catch anything that the known answer tests won't.
*/
goto end;
fail:
r = -1;
end:
return r;
}
/** Force the Ed25519 implementation to a given one, without sanity checking
* the output. Used for testing.
*/
void
ed25519_set_impl_params(int use_donna)
{
if (use_donna)
ed25519_impl = &impl_donna;
else
ed25519_impl = &impl_ref10;
}
/** Choose whether to use the Ed25519-donna implementation. */
static void
pick_ed25519_impl(void)
{
ed25519_impl = &impl_donna;
if (ed25519_impl_spot_check() == 0)
return;
/* LCOV_EXCL_START
* unreachable unless ed25519_donna is broken */
log_warn(LD_CRYPTO, "The Ed25519-donna implementation seems broken; using "
"the ref10 implementation.");
ed25519_impl = &impl_ref10;
/* LCOV_EXCL_STOP */
}
/* Initialize the Ed25519 implementation. This is neccessary if you're
* going to use them in a multithreaded setting, and not otherwise. */
void
ed25519_init(void)
{
pick_ed25519_impl();
}
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