From b6a7f794761a691aeae8d701b0fc14a9fed75471 Mon Sep 17 00:00:00 2001
From: Justus Winter <justus@sequoia-pgp.org>
Date: Tue, 19 Mar 2019 14:21:11 +0100
Subject: openpgp-ffi: New example.

---
 openpgp-ffi/examples/Makefile       |   1 +
 openpgp-ffi/examples/decrypt-with.c | 124 ++++++++++++++++++++++++++++++++++++
 2 files changed, 125 insertions(+)
 create mode 100644 openpgp-ffi/examples/decrypt-with.c

(limited to 'openpgp-ffi')

diff --git a/openpgp-ffi/examples/Makefile b/openpgp-ffi/examples/Makefile
index 35c4e9e8..77e5aad9 100644
--- a/openpgp-ffi/examples/Makefile
+++ b/openpgp-ffi/examples/Makefile
@@ -10,6 +10,7 @@ EXAMPLE_TARGET_DIR      ?= $(CARGO_TARGET_DIR)/debug/c-examples/openpgp-ffi
 
 EXAMPLES = \
 	example reader parser encrypt-for armor \
+	decrypt-with \
 	type-safety-demo use-after-free-demo immutable-reference-demo \
 
 CFLAGS  = -I../include -O0 -g -Wall -Werror
diff --git a/openpgp-ffi/examples/decrypt-with.c b/openpgp-ffi/examples/decrypt-with.c
new file mode 100644
index 00000000..b54de0fc
--- /dev/null
+++ b/openpgp-ffi/examples/decrypt-with.c
@@ -0,0 +1,124 @@
+/* This example demonstrates how to use the low-level interface to
+   decrypt a file.  */
+
+#define _GNU_SOURCE
+#include <assert.h>
+#include <error.h>
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include <sequoia/openpgp.h>
+
+struct decrypt_cookie {
+  pgp_tpk_t key;
+  int get_secret_keys_called;
+};
+
+static pgp_status_t
+get_public_keys_cb (void *cookie_raw,
+                    pgp_keyid_t *keyids, size_t keyids_len,
+                    pgp_tpk_t **tpks, size_t *tpk_len,
+                    void (**our_free)(void *))
+{
+  /* Feed the TPKs to the verifier here.  */
+  *tpks = NULL;
+  *tpk_len = 0;
+  *our_free = free;
+  return PGP_STATUS_SUCCESS;
+}
+
+static pgp_status_t
+check_signatures_cb(void *cookie_opaque,
+                   pgp_verification_results_t results, size_t levels)
+{
+  /* Implement your verification policy here.  */
+  return PGP_STATUS_SUCCESS;
+}
+
+static pgp_status_t
+get_secret_keys_cb (void *cookie_opaque,
+                    pgp_pkesk_t *pkesks, size_t pkesk_count,
+                    pgp_skesk_t *skesks, size_t skesk_count,
+                    pgp_secret_t *secret)
+{
+  pgp_error_t err;
+  struct decrypt_cookie *cookie = cookie_opaque;
+
+  /* Prevent iterations, we only have one key to offer.  */
+  if (cookie->get_secret_keys_called)
+    return PGP_STATUS_UNKNOWN_ERROR;
+  cookie->get_secret_keys_called = 1;
+
+  for (int i = 0; i < pkesk_count; i++) {
+    pgp_pkesk_t pkesk = pkesks[i];
+    pgp_keyid_t keyid = pgp_pkesk_recipient (pkesk);
+
+    pgp_tpk_key_iter_t key_iter = pgp_tpk_key_iter_all (cookie->key);
+    pgp_key_t key;
+    while ((key = pgp_tpk_key_iter_next (key_iter, NULL, NULL))) {
+      pgp_keyid_t this_keyid = pgp_key_keyid (key);
+      int match = pgp_keyid_equal (this_keyid, keyid);
+      pgp_keyid_free (this_keyid);
+      if (match)
+        break;
+      pgp_key_free (key);
+    }
+    pgp_tpk_key_iter_free (key_iter);
+    pgp_keyid_free (keyid);
+    if (! key)
+      continue;
+
+    uint8_t algo;
+    uint8_t session_key[1024];
+    size_t session_key_len = sizeof session_key;
+    if (pgp_pkesk_decrypt (&err,
+                           pkesk, key, &algo,
+                           session_key, &session_key_len)) {
+      error (1, 0, "pgp_pkesk_decrypt: %s", pgp_error_to_string (err));
+    }
+    pgp_key_free (key);
+
+    *secret = pgp_secret_cached (algo, session_key, session_key_len);
+    return PGP_STATUS_SUCCESS;
+  }
+
+  return PGP_STATUS_UNKNOWN_ERROR;
+}
+
+int
+main (int argc, char **argv)
+{
+  pgp_status_t rc;
+  pgp_error_t err;
+  pgp_tpk_t tpk;
+  pgp_reader_t source;
+  pgp_writer_t sink;
+
+  if (argc != 2)
+    error (1, 0, "Usage: %s <keyfile> <cipher >plain", argv[0]);
+
+  tpk = pgp_tpk_from_file (&err, argv[1]);
+  if (tpk == NULL)
+    error (1, 0, "pgp_tpk_from_file: %s", pgp_error_to_string (err));
+
+  source = pgp_reader_from_fd (STDIN_FILENO);
+  assert (source);
+  sink = pgp_writer_from_fd (STDOUT_FILENO);
+  assert (sink);
+
+  struct decrypt_cookie cookie = {
+    .key = tpk,
+    .get_secret_keys_called = 0,
+  };
+  rc = pgp_decrypt (&err, source, sink,
+                    get_public_keys_cb, get_secret_keys_cb,
+                    check_signatures_cb, &cookie);
+  if (rc)
+    error (1, 0, "pgp_decrypt: %s", pgp_error_to_string (err));
+
+  pgp_writer_free (sink);
+  pgp_reader_free (source);
+  pgp_tpk_free (tpk);
+  return 0;
+}
-- 
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