diff options
| -rw-r--r-- | PROTOCOL.u2f | 26 | ||||
| -rw-r--r-- | ssh-ecdsa-sk.c | 124 | ||||
| -rw-r--r-- | sshkey.c | 4 |
3 files changed, 144 insertions, 10 deletions
diff --git a/PROTOCOL.u2f b/PROTOCOL.u2f index 69347e99..fd31ea4e 100644 --- a/PROTOCOL.u2f +++ b/PROTOCOL.u2f @@ -209,6 +209,32 @@ For Ed25519 keys the signature is encoded as: byte flags uint32 counter +webauthn signatures +------------------- + +The W3C/FIDO webauthn[1] standard defines a mechanism for a web browser to +interact with FIDO authentication tokens. This standard builds upon the +FIDO standards, but requires different signature contents to raw FIDO +messages. OpenSSH supports ECDSA/p256 webauthn signatures through the +"webauthn-sk-ecdsa-sha2-nistp256@openssh.com" signature algorithm. + +The wire encoding for a webauthn-sk-ecdsa-sha2-nistp256@openssh.com +signature is similar to the sk-ecdsa-sha2-nistp256@openssh.com format: + + string "webauthn-sk-ecdsa-sha2-nistp256@openssh.com" + string ecdsa_signature + byte flags + uint32 counter + string origin + string clientData + string extensions + +Where "origin" is the HTTP origin making the signature, "clientData" is +the JSON-like structure signed by the browser and "extensions" are any +extensions used in making the signature. + +[1] https://www.w3.org/TR/webauthn-2/ + ssh-agent protocol extensions ----------------------------- diff --git a/ssh-ecdsa-sk.c b/ssh-ecdsa-sk.c index dcf605ba..0004a73c 100644 --- a/ssh-ecdsa-sk.c +++ b/ssh-ecdsa-sk.c @@ -1,4 +1,4 @@ -/* $OpenBSD: ssh-ecdsa-sk.c,v 1.6 2020/06/22 05:56:23 djm Exp $ */ +/* $OpenBSD: ssh-ecdsa-sk.c,v 1.7 2020/06/22 05:58:35 djm Exp $ */ /* * Copyright (c) 2000 Markus Friedl. All rights reserved. * Copyright (c) 2010 Damien Miller. All rights reserved. @@ -49,6 +49,87 @@ #define SSHKEY_INTERNAL #include "sshkey.h" +#ifndef OPENSSL_HAS_ECC +/* ARGSUSED */ +int +ssh_ecdsa_sk_verify(const struct sshkey *key, + const u_char *signature, size_t signaturelen, + const u_char *data, size_t datalen, u_int compat, + struct sshkey_sig_details **detailsp) +{ + return SSH_ERR_FEATURE_UNSUPPORTED; +} +#else /* OPENSSL_HAS_ECC */ + +/* + * Check FIDO/W3C webauthn signatures clientData field against the expected + * format and prepare a hash of it for use in signature verification. + * + * webauthn signatures do not sign the hash of the message directly, but + * instead sign a JSON-like "clientData" wrapper structure that contains the + * message hash along with a other information. + * + * Fortunately this structure has a fixed format so it is possible to verify + * that the hash of the signed message is present within the clientData + * structure without needing to implement any JSON parsing. + */ +static int +webauthn_check_prepare_hash(const u_char *data, size_t datalen, + const char *origin, const struct sshbuf *wrapper, + uint8_t flags, const struct sshbuf *extensions, + u_char *msghash, size_t msghashlen) +{ + int r = SSH_ERR_INTERNAL_ERROR; + struct sshbuf *chall = NULL, *m = NULL; + + if ((m = sshbuf_new()) == NULL || + (chall = sshbuf_from(data, datalen)) == NULL) { + r = SSH_ERR_ALLOC_FAIL; + goto out; + } + /* + * Ensure origin contains no quote character and that the flags are + * consistent with what we received + */ + if (strchr(origin, '\"') != NULL || + (flags & 0x40) != 0 /* AD */ || + ((flags & 0x80) == 0 /* ED */) != (sshbuf_len(extensions) == 0)) { + r = SSH_ERR_INVALID_FORMAT; + goto out; + } +#define WEBAUTHN_0 "{\"type\":\"webauthn.get\",\"challenge\":\"" +#define WEBAUTHN_1 "\",\"origin\":\"" +#define WEBAUTHN_2 "\"" + if ((r = sshbuf_put(m, WEBAUTHN_0, sizeof(WEBAUTHN_0) - 1)) != 0 || + (r = sshbuf_dtourlb64(chall, m, 0)) != 0 || + (r = sshbuf_put(m, WEBAUTHN_1, sizeof(WEBAUTHN_1) - 1)) != 0 || + (r = sshbuf_put(m, origin, strlen(origin))) != 0 || + (r = sshbuf_put(m, WEBAUTHN_2, sizeof(WEBAUTHN_2) - 1)) != 0) + goto out; +#ifdef DEBUG_SK + fprintf(stderr, "%s: received origin: %s\n", __func__, origin); + fprintf(stderr, "%s: received clientData:\n", __func__); + sshbuf_dump(wrapper, stderr); + fprintf(stderr, "%s: expected clientData premable:\n", __func__); + sshbuf_dump(m, stderr); +#endif + /* Check that the supplied clientData matches what we expect */ + if ((r = sshbuf_cmp(wrapper, 0, sshbuf_ptr(m), sshbuf_len(m))) != 0) + goto out; + + /* Prepare hash of clientData */ + if ((r = ssh_digest_buffer(SSH_DIGEST_SHA256, wrapper, + msghash, msghashlen)) != 0) + goto out; + + /* success */ + r = 0; + out: + sshbuf_free(chall); + sshbuf_free(m); + return r; +} + /* ARGSUSED */ int ssh_ecdsa_sk_verify(const struct sshkey *key, @@ -56,15 +137,15 @@ ssh_ecdsa_sk_verify(const struct sshkey *key, const u_char *data, size_t datalen, u_int compat, struct sshkey_sig_details **detailsp) { -#ifdef OPENSSL_HAS_ECC ECDSA_SIG *sig = NULL; BIGNUM *sig_r = NULL, *sig_s = NULL; u_char sig_flags; u_char msghash[32], apphash[32], sighash[32]; u_int sig_counter; - int ret = SSH_ERR_INTERNAL_ERROR; + int is_webauthn = 0, ret = SSH_ERR_INTERNAL_ERROR; struct sshbuf *b = NULL, *sigbuf = NULL, *original_signed = NULL; - char *ktype = NULL; + struct sshbuf *webauthn_wrapper = NULL, *webauthn_exts = NULL; + char *ktype = NULL, *webauthn_origin = NULL; struct sshkey_sig_details *details = NULL; #ifdef DEBUG_SK char *tmp = NULL; @@ -91,7 +172,9 @@ ssh_ecdsa_sk_verify(const struct sshkey *key, ret = SSH_ERR_INVALID_FORMAT; goto out; } - if (strcmp(ktype, "sk-ecdsa-sha2-nistp256@openssh.com") != 0) { + if (strcmp(ktype, "webauthn-sk-ecdsa-sha2-nistp256@openssh.com") == 0) + is_webauthn = 1; + else if (strcmp(ktype, "sk-ecdsa-sha2-nistp256@openssh.com") != 0) { ret = SSH_ERR_INVALID_FORMAT; goto out; } @@ -101,6 +184,14 @@ ssh_ecdsa_sk_verify(const struct sshkey *key, ret = SSH_ERR_INVALID_FORMAT; goto out; } + if (is_webauthn) { + if (sshbuf_get_cstring(b, &webauthn_origin, NULL) != 0 || + sshbuf_froms(b, &webauthn_wrapper) != 0 || + sshbuf_froms(b, &webauthn_exts) != 0) { + ret = SSH_ERR_INVALID_FORMAT; + goto out; + } + } if (sshbuf_len(b) != 0) { ret = SSH_ERR_UNEXPECTED_TRAILING_DATA; goto out; @@ -116,6 +207,7 @@ ssh_ecdsa_sk_verify(const struct sshkey *key, ret = SSH_ERR_UNEXPECTED_TRAILING_DATA; goto out; } + #ifdef DEBUG_SK fprintf(stderr, "%s: data: (len %zu)\n", __func__, datalen); /* sshbuf_dump_data(data, datalen, stderr); */ @@ -125,6 +217,12 @@ ssh_ecdsa_sk_verify(const struct sshkey *key, free(tmp); fprintf(stderr, "%s: sig_flags = 0x%02x, sig_counter = %u\n", __func__, sig_flags, sig_counter); + if (is_webauthn) { + fprintf(stderr, "%s: webauthn origin: %s\n", __func__, + webauthn_origin); + fprintf(stderr, "%s: webauthn_wrapper:\n", __func__); + sshbuf_dump(webauthn_wrapper, stderr); + } #endif if ((sig = ECDSA_SIG_new()) == NULL) { ret = SSH_ERR_ALLOC_FAIL; @@ -141,7 +239,12 @@ ssh_ecdsa_sk_verify(const struct sshkey *key, ret = SSH_ERR_ALLOC_FAIL; goto out; } - if ((ret = ssh_digest_memory(SSH_DIGEST_SHA256, data, datalen, + if (is_webauthn) { + if ((ret = webauthn_check_prepare_hash(data, datalen, + webauthn_origin, webauthn_wrapper, sig_flags, webauthn_exts, + msghash, sizeof(msghash))) != 0) + goto out; + } else if ((ret = ssh_digest_memory(SSH_DIGEST_SHA256, data, datalen, msghash, sizeof(msghash))) != 0) goto out; /* Application value is hashed before signature */ @@ -158,6 +261,7 @@ ssh_ecdsa_sk_verify(const struct sshkey *key, apphash, sizeof(apphash))) != 0 || (ret = sshbuf_put_u8(original_signed, sig_flags)) != 0 || (ret = sshbuf_put_u32(original_signed, sig_counter)) != 0 || + (ret = sshbuf_putb(original_signed, webauthn_exts)) != 0 || (ret = sshbuf_put(original_signed, msghash, sizeof(msghash))) != 0) goto out; /* Signature is over H(original_signed) */ @@ -197,6 +301,9 @@ ssh_ecdsa_sk_verify(const struct sshkey *key, explicit_bzero(sighash, sizeof(msghash)); explicit_bzero(apphash, sizeof(apphash)); sshkey_sig_details_free(details); + sshbuf_free(webauthn_wrapper); + sshbuf_free(webauthn_exts); + free(webauthn_origin); sshbuf_free(original_signed); sshbuf_free(sigbuf); sshbuf_free(b); @@ -205,7 +312,6 @@ ssh_ecdsa_sk_verify(const struct sshkey *key, BN_clear_free(sig_s); free(ktype); return ret; -#else - return SSH_ERR_INTERNAL_ERROR; -#endif } + +#endif /* OPENSSL_HAS_ECC */ @@ -1,4 +1,4 @@ -/* $OpenBSD: sshkey.c,v 1.108 2020/04/11 10:16:11 djm Exp $ */ +/* $OpenBSD: sshkey.c,v 1.109 2020/06/22 05:58:35 djm Exp $ */ /* * Copyright (c) 2000, 2001 Markus Friedl. All rights reserved. * Copyright (c) 2008 Alexander von Gernler. All rights reserved. @@ -132,6 +132,8 @@ static const struct keytype keytypes[] = { # endif /* OPENSSL_HAS_NISTP521 */ { "sk-ecdsa-sha2-nistp256@openssh.com", "ECDSA-SK", NULL, KEY_ECDSA_SK, NID_X9_62_prime256v1, 0, 0 }, + { "webauthn-sk-ecdsa-sha2-nistp256@openssh.com", "ECDSA-SK", NULL, + KEY_ECDSA_SK, NID_X9_62_prime256v1, 0, 1 }, # endif /* OPENSSL_HAS_ECC */ { "ssh-rsa-cert-v01@openssh.com", "RSA-CERT", NULL, KEY_RSA_CERT, 0, 1, 0 }, |