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

1 files changed, 78 insertions, 0 deletions

diff --git a/sshsig.h b/sshsig.h
new file mode 100644
index 00000000..92c675e3
--- /dev/null
+++ b/sshsig.h
@@ -0,0 +1,78 @@
+/*
+ * Copyright (c) 2019 Google LLC
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#ifndef SSHSIG_H
+#define SSHSIG_H
+
+struct sshbuf;
+struct sshkey;
+
+typedef int sshsig_signer(struct sshkey *, u_char **, size_t *,
+    const u_char *, size_t, const char *, u_int, void *);
+
+/*
+ * Creates a detached SSH signature for a given message.
+ * Returns 0 on success or a negative SSH_ERR_* error code on failure.
+ * out is populated with the detached signature, or NULL on failure.
+ */
+int sshsig_sign_message(struct sshkey *key, const char *hashalg,
+    const struct sshbuf *message, const char *sig_namespace,
+    struct sshbuf **out, sshsig_signer *signer, void *signer_ctx);
+
+/*
+ * Creates a detached SSH signature for a given file.
+ * Returns 0 on success or a negative SSH_ERR_* error code on failure.
+ * out is populated with the detached signature, or NULL on failure.
+ */
+int sshsig_sign_fd(struct sshkey *key, const char *hashalg,
+    int fd, const char *sig_namespace, struct sshbuf **out,
+    sshsig_signer *signer, void *signer_ctx);
+
+/*
+ * Verifies that a detached signature is valid and optionally returns key
+ * used to sign via argument.
+ * Returns 0 on success or a negative SSH_ERR_* error code on failure.
+ */
+int sshsig_verify_message(struct sshbuf *signature,
+    const struct sshbuf *message, const char *sig_namespace,
+    struct sshkey **sign_keyp);
+
+/*
+ * Verifies that a detached signature over a file is valid and optionally
+ * returns key used to sign via argument.
+ * Returns 0 on success or a negative SSH_ERR_* error code on failure.
+ */
+int sshsig_verify_fd(struct sshbuf *signature, int fd,
+    const char *sig_namespace, struct sshkey **sign_keyp);
+
+/*
+ * Return a base64 encoded "ASCII armoured" version of a raw signature.
+ */
+int sshsig_armor(const struct sshbuf *blob, struct sshbuf **out);
+
+/*
+ * Decode a base64 encoded armoured signature to a raw signature.
+ */
+int sshsig_dearmor(struct sshbuf *sig, struct sshbuf **out);
+
+/*
+ * Checks whether a particular key/principal/namespace is permitted by
+ * an allowed_keys file. Returns 0 on success.
+ */
+int sshsig_check_allowed_keys(const char *path, const struct sshkey *sign_key,
+    const char *principal, const char *ns);
+
+#endif /* SSHSIG_H */