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upstream: when signing a challenge using a FIDO toke, perform the 

hashing in the middleware layer rather than in ssh code. This allows
middlewares that call APIs that perform the hashing implicitly (including
Microsoft's AFAIK). ok markus@

OpenBSD-Commit-ID: c9fc8630aba26c75d5016884932f08a5a237f37d
This commit is contained in:
djm@openbsd.org 2020-04-28 04:02:29 +00:00 committed by Damien Miller
parent c9d10dbc0c
commit 59d2de956e
4 changed files with 37 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
PROTOCOL.u2f
View File

@ -236,7 +236,7 @@ support for the common case of USB HID security keys internally.
The middleware library need only expose a handful of functions:
#define SSH_SK_VERSION_MAJOR 0x00040000 /* API version */
#define SSH_SK_VERSION_MAJOR 0x00050000 /* API version */
#define SSH_SK_VERSION_MAJOR_MASK 0xffff0000
/* Flags */

4
sk-api.h
View File

@ -1,4 +1,4 @@
/* $OpenBSD: sk-api.h,v 1.8 2020/01/25 23:13:09 djm Exp $ */
/* $OpenBSD: sk-api.h,v 1.9 2020/04/28 04:02:29 djm Exp $ */
/*
* Copyright (c) 2019 Google LLC
*
@ -71,7 +71,7 @@ struct sk_option {
uint8_t required;
};
#define SSH_SK_VERSION_MAJOR 0x00040000 /* current API version */
#define SSH_SK_VERSION_MAJOR 0x00050000 /* current API version */
#define SSH_SK_VERSION_MAJOR_MASK 0xffff0000
/* Return the version of the middleware API */

35
sk-usbhid.c
View File

@ -24,6 +24,7 @@
#include <stdio.h>
#include <stddef.h>
#include <stdarg.h>
#include <sha2.h>
#ifdef WITH_OPENSSL
#include <openssl/opensslv.h>
@ -31,6 +32,7 @@
#include <openssl/bn.h>
#include <openssl/ec.h>
#include <openssl/ecdsa.h>
#include <openssl/evp.h>
#endif /* WITH_OPENSSL */
#include <fido.h>
@ -710,8 +712,28 @@ check_sign_load_resident_options(struct sk_option **options, char **devicep)
return 0;
}
/* Calculate SHA256(m) */
static int
sha256_mem(const void *m, size_t mlen, u_char *d, size_t dlen)
{
#ifdef WITH_OPENSSL
u_int mdlen;
#endif
if (dlen != 32)
return -1;
#ifdef WITH_OPENSSL
mdlen = dlen;
if (!EVP_Digest(m, mlen, d, &mdlen, EVP_sha256(), NULL))
return -1;
#else
SHA256Data(m, mlen, d);
#endif
return 0;
}
int
sk_sign(uint32_t alg, const uint8_t *message, size_t message_len,
sk_sign(uint32_t alg, const uint8_t *data, size_t datalen,
const char *application,
const uint8_t *key_handle, size_t key_handle_len,
uint8_t flags, const char *pin, struct sk_option **options,
@ -721,6 +743,7 @@ sk_sign(uint32_t alg, const uint8_t *message, size_t message_len,
char *device = NULL;
fido_dev_t *dev = NULL;
struct sk_sign_response *response = NULL;
uint8_t message[32];
int ret = SSH_SK_ERR_GENERAL;
int r;
@ -735,7 +758,12 @@ sk_sign(uint32_t alg, const uint8_t *message, size_t message_len,
*sign_response = NULL;
if (check_sign_load_resident_options(options, &device) != 0)
goto out; /* error already logged */
if ((dev = find_device(device, message, message_len,
/* hash data to be signed before it goes to the security key */
if ((r = sha256_mem(data, datalen, message, sizeof(message))) != 0) {
skdebug(__func__, "hash message failed");
goto out;
}
if ((dev = find_device(device, message, sizeof(message),
application, key_handle, key_handle_len)) == NULL) {
skdebug(__func__, "couldn't find device for key handle");
goto out;
@ -745,7 +773,7 @@ sk_sign(uint32_t alg, const uint8_t *message, size_t message_len,
goto out;
}
if ((r = fido_assert_set_clientdata_hash(assert, message,
message_len)) != FIDO_OK) {
sizeof(message))) != FIDO_OK) {
skdebug(__func__, "fido_assert_set_clientdata_hash: %s",
fido_strerr(r));
goto out;
@ -783,6 +811,7 @@ sk_sign(uint32_t alg, const uint8_t *message, size_t message_len,
response = NULL;
ret = 0;
out:
explicit_bzero(message, sizeof(message));
free(device);
if (response != NULL) {
free(response->sig_r);

14
ssh-sk.c
View File

@ -1,4 +1,4 @@
/* $OpenBSD: ssh-sk.c,v 1.29 2020/03/06 18:25:48 markus Exp $ */
/* $OpenBSD: ssh-sk.c,v 1.30 2020/04/28 04:02:29 djm Exp $ */
/*
* Copyright (c) 2019 Google LLC
*
@ -615,7 +615,6 @@ sshsk_sign(const char *provider_path, struct sshkey *key,
int type, alg;
struct sk_sign_response *resp = NULL;
struct sshbuf *inner_sig = NULL, *sig = NULL;
uint8_t message[32];
struct sk_option **opts = NULL;
debug("%s: provider \"%s\", key %s, flags 0x%02x%s", __func__,
@ -650,15 +649,7 @@ sshsk_sign(const char *provider_path, struct sshkey *key,
goto out;
}
/* hash data to be signed before it goes to the security key */
if ((r = ssh_digest_memory(SSH_DIGEST_SHA256, data, datalen,
message, sizeof(message))) != 0) {
error("%s: hash application failed: %s", __func__, ssh_err(r));
r = SSH_ERR_INTERNAL_ERROR;
goto out;
}
if ((r = skp->sk_sign(alg, message, sizeof(message),
key->sk_application,
if ((r = skp->sk_sign(alg, data, datalen, key->sk_application,
sshbuf_ptr(key->sk_key_handle), sshbuf_len(key->sk_key_handle),
key->sk_flags, pin, opts, &resp)) != 0) {
debug("%s: sk_sign failed with code %d", __func__, r);
@ -707,7 +698,6 @@ sshsk_sign(const char *provider_path, struct sshkey *key,
r = 0;
out:
sshsk_free_options(opts);
explicit_bzero(message, sizeof(message));
sshsk_free(skp);
sshsk_free_sign_response(resp);
sshbuf_free(sig);