[image] Add the "imgdecrypt" command

Add the "imgdecrypt" command that can be used to decrypt a detached
encrypted data image using a cipher key obtained from a separate CMS
envelope image.  For example:

  # Create non-detached encrypted CMS messages
  #
  openssl cms -encrypt -binary -aes-256-gcm -recip client.crt \
              -in vmlinuz -outform DER -out vmlinuz.cms
  openssl cms -encrypt -binary -aes-256-gcm -recip client.crt \
              -in initrd.img -outform DER -out initrd.img.cms

  # Detach data from envelopes (using iPXE's contrib/crypto/cmsdetach)
  #
  cmsdetach vmlinuz.cms -d vmlinuz.dat -e vmlinuz.env
  cmsdetach initrd.img.cms -d initrd.img.dat -e initrd.img.env

and then within iPXE:

  #!ipxe
  imgfetch http://192.168.0.1/vmlinuz.dat
  imgfetch http://192.168.0.1/initrd.img.dat
  imgdecrypt vmlinuz.dat    http://192.168.0.1/vmlinuz.env
  imgdecrypt initrd.img.dat http://192.168.0.1/initrd.img.env
  boot vmlinuz

Signed-off-by: Michael Brown <mcb30@ipxe.org>

1 files changed, 75 insertions, 0 deletions

diff --git a/src/usr/imgcrypt.c b/src/usr/imgcrypt.c
new file mode 100644
index 000000000..1b649f197
--- /dev/null
+++ b/src/usr/imgcrypt.c
@@ -0,0 +1,75 @@
+/*
+ * Copyright (C) 2024 Michael Brown <mbrown@fensystems.co.uk>.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ *
+ * You can also choose to distribute this program under the terms of
+ * the Unmodified Binary Distribution Licence (as given in the file
+ * COPYING.UBDL), provided that you have satisfied its requirements.
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+#include <string.h>
+#include <syslog.h>
+#include <ipxe/image.h>
+#include <ipxe/cms.h>
+#include <ipxe/privkey.h>
+#include <usr/imgcrypt.h>
+
+/** @file
+ *
+ * Image encryption management
+ *
+ */
+
+/**
+ * Decrypt image using downloaded envelope
+ *
+ * @v image		Image to decrypt
+ * @v envelope		Image containing decryption key
+ * @v name		Decrypted image name (or NULL to use default)
+ * @ret rc		Return status code
+ */
+int imgdecrypt ( struct image *image, struct image *envelope,
+		 const char *name ) {
+	struct cms_message *cms;
+	int rc;
+
+	/* Parse envelope */
+	if ( ( rc = cms_message ( envelope, &cms ) ) != 0 )
+		goto err_parse;
+
+	/* Decrypt image */
+	if ( ( rc = cms_decrypt ( cms, image, name, &private_key ) ) != 0 )
+		goto err_decrypt;
+
+	/* Drop reference to message */
+	cms_put ( cms );
+	cms = NULL;
+
+	/* Record decryption */
+	syslog ( LOG_NOTICE, "Image \"%s\" decrypted OK\n", image->name );
+
+	return 0;
+
+ err_decrypt:
+	cms_put ( cms );
+ err_parse:
+	syslog ( LOG_ERR, "Image \"%s\" decryption failed: %s\n",
+		 image->name, strerror ( rc ) );
+	return rc;
+}