From 2a9c9f7272c1e8665155118fe6536bebdafb6166 Mon Sep 17 00:00:00 2001 From: "djm@openbsd.org" Date: Tue, 3 Sep 2019 08:34:19 +0000 Subject: upstream: sshsig: lightweight signature and verification ability for OpenSSH This adds a simple manual signature scheme to OpenSSH. Signatures can be made and verified using ssh-keygen -Y sign|verify Signatures embed the key used to make them. At verification time, this is matched via principal name against an authorized_keys-like list of allowed signers. Mostly by Sebastian Kinne w/ some tweaks by me ok markus@ OpenBSD-Commit-ID: 2ab568e7114c933346616392579d72be65a4b8fb --- ssh-keygen.c | 325 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 321 insertions(+), 4 deletions(-) (limited to 'ssh-keygen.c') diff --git a/ssh-keygen.c b/ssh-keygen.c index 3c32513bf..76bc41b2f 100644 --- a/ssh-keygen.c +++ b/ssh-keygen.c @@ -1,4 +1,4 @@ -/* $OpenBSD: ssh-keygen.c,v 1.343 2019/09/03 08:27:52 djm Exp $ */ +/* $OpenBSD: ssh-keygen.c,v 1.344 2019/09/03 08:34:19 djm Exp $ */ /* * Author: Tatu Ylonen * Copyright (c) 1994 Tatu Ylonen , Espoo, Finland @@ -59,6 +59,7 @@ #include "digest.h" #include "utf8.h" #include "authfd.h" +#include "sshsig.h" #ifdef WITH_OPENSSL # define DEFAULT_KEY_TYPE_NAME "rsa" @@ -2422,6 +2423,279 @@ do_check_krl(struct passwd *pw, int argc, char **argv) exit(ret); } +static struct sshkey * +load_sign_key(const char *keypath, const struct sshkey *pubkey) +{ + size_t i, slen, plen = strlen(keypath); + char *privpath = xstrdup(keypath); + const char *suffixes[] = { "-cert.pub", ".pub", NULL }; + struct sshkey *ret = NULL, *privkey = NULL; + int r; + + /* + * If passed a public key filename, then try to locate the correponding + * private key. This lets us specify certificates on the command-line + * and have ssh-keygen find the appropriate private key. + */ + for (i = 0; suffixes[i]; i++) { + slen = strlen(suffixes[i]); + if (plen <= slen || + strcmp(privpath + plen - slen, suffixes[i]) != 0) + continue; + privpath[plen - slen] = '\0'; + debug("%s: %s looks like a public key, using private key " + "path %s instead", __func__, keypath, privpath); + } + if ((privkey = load_identity(privpath, NULL)) == NULL) { + error("Couldn't load identity %s", keypath); + goto done; + } + if (!sshkey_equal_public(pubkey, privkey)) { + error("Public key %s doesn't match private %s", + keypath, privpath); + goto done; + } + if (sshkey_is_cert(pubkey) && !sshkey_is_cert(privkey)) { + /* + * Graft the certificate onto the private key to make + * it capable of signing. + */ + if ((r = sshkey_to_certified(privkey)) != 0) { + error("%s: sshkey_to_certified: %s", __func__, + ssh_err(r)); + goto done; + } + if ((r = sshkey_cert_copy(pubkey, privkey)) != 0) { + error("%s: sshkey_cert_copy: %s", __func__, ssh_err(r)); + goto done; + } + } + /* success */ + ret = privkey; + privkey = NULL; + done: + sshkey_free(privkey); + free(privpath); + return ret; +} + +static int +sign_one(struct sshkey *signkey, const char *filename, int fd, + const char *sig_namespace, sshsig_signer *signer, void *signer_ctx) +{ + struct sshbuf *sigbuf = NULL, *abuf = NULL; + int r = SSH_ERR_INTERNAL_ERROR, wfd = -1, oerrno; + char *wfile = NULL; + char *asig = NULL; + + if (!quiet) { + if (fd == STDIN_FILENO) + fprintf(stderr, "Signing data on standard input\n"); + else + fprintf(stderr, "Signing file %s\n", filename); + } + if ((r = sshsig_sign_fd(signkey, NULL, fd, sig_namespace, + &sigbuf, signer, signer_ctx)) != 0) { + error("Signing %s failed: %s", filename, ssh_err(r)); + goto out; + } + if ((r = sshsig_armor(sigbuf, &abuf)) != 0) { + error("%s: sshsig_armor: %s", __func__, ssh_err(r)); + goto out; + } + if ((asig = sshbuf_dup_string(abuf)) == NULL) { + error("%s: buffer error", __func__); + r = SSH_ERR_ALLOC_FAIL; + goto out; + } + + if (fd == STDIN_FILENO) { + fputs(asig, stdout); + fflush(stdout); + } else { + xasprintf(&wfile, "%s.sig", filename); + if (confirm_overwrite(wfile)) { + if ((wfd = open(wfile, O_WRONLY|O_CREAT|O_TRUNC, + 0666)) == -1) { + oerrno = errno; + error("Cannot open %s: %s", + wfile, strerror(errno)); + errno = oerrno; + r = SSH_ERR_SYSTEM_ERROR; + goto out; + } + if (atomicio(vwrite, wfd, asig, + strlen(asig)) != strlen(asig)) { + oerrno = errno; + error("Cannot write to %s: %s", + wfile, strerror(errno)); + errno = oerrno; + r = SSH_ERR_SYSTEM_ERROR; + goto out; + } + if (!quiet) { + fprintf(stderr, "Write signature to %s\n", + wfile); + } + } + } + /* success */ + r = 0; + out: + free(wfile); + free(asig); + sshbuf_free(abuf); + sshbuf_free(sigbuf); + if (wfd != -1) + close(wfd); + return r; +} + +static int +sign(const char *keypath, const char *sig_namespace, int argc, char **argv) +{ + int i, fd = -1, r, ret = -1; + int agent_fd = -1; + struct sshkey *pubkey = NULL, *privkey = NULL, *signkey = NULL; + sshsig_signer *signer = NULL; + + /* Check file arguments. */ + for (i = 0; i < argc; i++) { + if (strcmp(argv[i], "-") != 0) + continue; + if (i > 0 || argc > 1) + fatal("Cannot sign mix of paths and standard input"); + } + + if ((r = sshkey_load_public(keypath, &pubkey, NULL)) != 0) { + error("Couldn't load public key %s: %s", keypath, ssh_err(r)); + goto done; + } + + if ((r = ssh_get_authentication_socket(&agent_fd)) != 0) + debug("Couldn't get agent socket: %s", ssh_err(r)); + else { + if ((r = ssh_agent_has_key(agent_fd, pubkey)) == 0) + signer = agent_signer; + else + debug("Couldn't find key in agent: %s", ssh_err(r)); + } + + if (signer == NULL) { + /* Not using agent - try to load private key */ + if ((privkey = load_sign_key(keypath, pubkey)) == NULL) + goto done; + signkey = privkey; + } else { + /* Will use key in agent */ + signkey = pubkey; + } + + if (argc == 0) { + if ((r = sign_one(signkey, "(stdin)", STDIN_FILENO, + sig_namespace, signer, &agent_fd)) != 0) + goto done; + } else { + for (i = 0; i < argc; i++) { + if (strcmp(argv[i], "-") == 0) + fd = STDIN_FILENO; + else if ((fd = open(argv[i], O_RDONLY)) == -1) { + error("Cannot open %s for signing: %s", + argv[i], strerror(errno)); + goto done; + } + if ((r = sign_one(signkey, argv[i], fd, sig_namespace, + signer, &agent_fd)) != 0) + goto done; + if (fd != STDIN_FILENO) + close(fd); + fd = -1; + } + } + + ret = 0; +done: + if (fd != -1 && fd != STDIN_FILENO) + close(fd); + sshkey_free(pubkey); + sshkey_free(privkey); + return ret; +} + +static int +verify(const char *signature, const char *sig_namespace, const char *principal, + const char *allowed_keys, const char *revoked_keys) +{ + int r, ret = -1, sigfd = -1; + struct sshbuf *sigbuf = NULL, *abuf = NULL; + struct sshkey *sign_key = NULL; + char *fp = NULL; + + if ((abuf = sshbuf_new()) == NULL) + fatal("%s: sshbuf_new() failed", __func__); + + if ((sigfd = open(signature, O_RDONLY)) < 0) { + error("Couldn't open signature file %s", signature); + goto done; + } + + if ((r = sshkey_load_file(sigfd, abuf)) != 0) { + error("Couldn't read signature file: %s", ssh_err(r)); + goto done; + } + if ((r = sshsig_dearmor(abuf, &sigbuf)) != 0) { + error("%s: sshsig_armor: %s", __func__, ssh_err(r)); + return r; + } + if ((r = sshsig_verify_fd(sigbuf, STDIN_FILENO, sig_namespace, + &sign_key)) != 0) + goto done; /* sshsig_verify() prints error */ + + if ((fp = sshkey_fingerprint(sign_key, fingerprint_hash, + SSH_FP_DEFAULT)) == NULL) + fatal("%s: sshkey_fingerprint failed", __func__); + debug("Valid (unverified) signature from key %s", fp); + free(fp); + fp = NULL; + + if (revoked_keys != NULL) { + if ((r = sshkey_check_revoked(sign_key, revoked_keys)) != 0) { + debug3("sshkey_check_revoked failed: %s", ssh_err(r)); + goto done; + } + } + + if ((r = sshsig_check_allowed_keys(allowed_keys, sign_key, + principal, sig_namespace)) != 0) { + debug3("sshsig_check_allowed_keys failed: %s", ssh_err(r)); + goto done; + } + /* success */ + ret = 0; +done: + if (!quiet) { + if (ret == 0) { + if ((fp = sshkey_fingerprint(sign_key, fingerprint_hash, + SSH_FP_DEFAULT)) == NULL) { + fatal("%s: sshkey_fingerprint failed", + __func__); + } + printf("Good \"%s\" signature for %s with %s key %s\n", + sig_namespace, principal, + sshkey_type(sign_key), fp); + } else { + printf("Could not verify signature.\n"); + } + } + if (sigfd != -1) + close(sigfd); + sshbuf_free(sigbuf); + sshbuf_free(abuf); + sshkey_free(sign_key); + free(fp); + return ret; +} + static void usage(void) { @@ -2457,7 +2731,10 @@ usage(void) " ssh-keygen -A\n" " ssh-keygen -k -f krl_file [-u] [-s ca_public] [-z version_number]\n" " file ...\n" - " ssh-keygen -Q -f krl_file file ...\n"); + " ssh-keygen -Q -f le file ...\n" + " ssh-keygen -Y sign -f sign_key -n namespace\n" + " ssh-keygen -Y verify -I signer_identity -s signature_file\n" + " -n namespace -f allowed_keys [-r revoked_keys]\n"); exit(1); } @@ -2484,6 +2761,7 @@ main(int argc, char **argv) FILE *f; const char *errstr; int log_level = SYSLOG_LEVEL_INFO; + char *sign_op = NULL; #ifdef WITH_OPENSSL /* Moduli generation/screening */ char out_file[PATH_MAX], *checkpoint = NULL; @@ -2514,9 +2792,9 @@ main(int argc, char **argv) if (gethostname(hostname, sizeof(hostname)) == -1) fatal("gethostname: %s", strerror(errno)); - /* Remaining characters: Ydw */ + /* Remaining characters: dw */ while ((opt = getopt(argc, argv, "ABHLQUXceghiklopquvxy" - "C:D:E:F:G:I:J:K:M:N:O:P:R:S:T:V:W:Z:" + "C:D:E:F:G:I:J:K:M:N:O:P:R:S:T:V:W:Y:Z:" "a:b:f:g:j:m:n:r:s:t:z:")) != -1) { switch (opt) { case 'A': @@ -2672,6 +2950,9 @@ main(int argc, char **argv) case 'V': parse_cert_times(optarg); break; + case 'Y': + sign_op = optarg; + break; case 'z': errno = 0; if (*optarg == '+') { @@ -2739,6 +3020,42 @@ main(int argc, char **argv) argv += optind; argc -= optind; + if (sign_op != NULL) { + if (cert_principals == NULL) { + error("Too few arguments for sign/verify: " + "missing namespace"); + exit(1); + } + if (strncmp(sign_op, "sign", 4) == 0) { + if (!have_identity) { + error("Too few arguments for sign: " + "missing key"); + exit(1); + } + return sign(identity_file, cert_principals, argc, argv); + } else if (strncmp(sign_op, "verify", 6) == 0) { + if (ca_key_path == NULL) { + error("Too few arguments for verify: " + "missing signature file"); + exit(1); + } + if (!have_identity) { + error("Too few arguments for sign: " + "missing allowed keys file"); + exit(1); + } + if (cert_key_id == NULL) { + error("Too few arguments for verify: " + "missing principal ID"); + exit(1); + } + return verify(ca_key_path, cert_principals, + cert_key_id, identity_file, rr_hostname); + } + usage(); + /* NOTREACHED */ + } + if (ca_key_path != NULL) { if (argc < 1 && !gen_krl) { error("Too few arguments."); -- cgit v1.2.3