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diff --git a/mailnews/mime/src/mimecryp.h b/mailnews/mime/src/mimecryp.h
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+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef _MIMECRYP_H_
+#define _MIMECRYP_H_
+
+#include "mimecont.h"
+// #include "mimeenc.h"
+#include "modmimee.h"
+#include "mimepbuf.h"
+
+/* The MimeEncrypted class implements a type of MIME object where the object
+   is passed to some other routine, which then returns a new MIME object.
+   This is the basis of a decryption module.
+
+   Oddly, this class behaves both as a container and as a leaf: it acts as a
+   container in that it parses out data in order to eventually present a
+   contained object; however, it acts as a leaf in that this container may
+   itself have a Content-Transfer-Encoding applied to its body.  This violates
+   the cardinal rule of MIME containers, which is that encodings don't nest,
+   and therefore containers can't have encodings.  But, the fact that the
+   S/MIME spec doesn't follow the groundwork laid down by previous MIME specs
+   isn't something we can do anything about at this point...
+
+   Therefore, this class duplicates some of the work done by the MimeLeaf
+   class, to meet its dual goals of container-hood and leaf-hood.  (We could
+   alternately have made this class be a subclass of leaf, and had it duplicate
+   the effort of MimeContainer, but that seemed like the harder approach.)
+
+   The MimeEncrypted class provides the following methods:
+
+   void *crypto_init(MimeObject *obj,
+           int (*output_fn) (const char *data, int32 data_size,
+                     void *output_closure),
+           void *output_closure)
+
+     This is called with the MimeObject representing the encrypted data.
+   The obj->headers should be used to initialize the decryption engine.
+   NULL indicates failure; otherwise, an opaque closure object should
+   be returned.
+
+   output_fn is what the decryption module should use to write a new MIME
+   object (the decrypted data.)  output_closure should be passed along to
+   every call to the output routine.
+
+   The data sent to output_fn should begin with valid MIME headers indicating
+   the type of the data.  For example, if decryption resulted in a text
+   document, the data fed through to the output_fn might minimally look like
+
+        Content-Type: text/plain
+
+        This is the decrypted data.
+        It is only two lines long.
+
+     Of course, the data may be of any MIME type, including multipart/mixed.
+   Any returned MIME object will be recursively processed and presented
+   appropriately.  (This also imples that encrypted objects may nest, and
+   thus that the underlying decryption module must be reentrant.)
+
+   int crypto_write (const char *data, int32 data_size, void *crypto_closure)
+
+     This is called with the raw encrypted data.  This data might not come
+   in line-based chunks: if there was a Content-Transfer-Encoding applied
+   to the data (base64 or quoted-printable) then it will have been decoded
+   first (handing binary data to the filter_fn.)  `crypto_closure' is the
+   object that `crypto_init' returned.  This may return negative on error.
+
+   int crypto_eof (void *crypto_closure, bool abort_p)
+
+     This is called when no more data remains.  It may call `output_fn' again
+   to flush out any buffered data.  If `abort_p' is true, then it may choose
+   to discard any data rather than processing it, as we're terminating
+   abnormally.
+
+   char * crypto_generate_html (void *crypto_closure)
+
+     This is called after `crypto_eof' but before `crypto_free'.  The crypto
+   module should return a newly-allocated string of HTML code which
+   explains the status of the decryption to the user (whether the signature
+   checked out, etc.)
+
+   void crypto_free (void *crypto_closure)
+
+     This will be called when we're all done, after `crypto_eof' and
+   `crypto_emit_html'.  It is intended to free any data represented
+   by the crypto_closure.  output_fn may not be called.
+
+
+   int (*parse_decoded_buffer) (const char *buf, int32 size, MimeObject *obj)
+
+     This method, of the same name as one in MimeLeaf, is a part of the
+   afforementioned leaf/container hybridization.  This method is invoked
+   with the content-transfer-decoded body of this part (without line
+   buffering.)  The default behavior of this method is to simply invoke
+   `crypto_write' on the data with which it is called.  It's unlikely that
+   a subclass will need to specialize this.
+ */
+
+typedef struct MimeEncryptedClass MimeEncryptedClass;
+typedef struct MimeEncrypted      MimeEncrypted;
+
+struct MimeEncryptedClass {
+  MimeContainerClass container;
+
+  /* Duplicated from MimeLeaf, see comments above.
+     This is the callback that is handed to the decoder. */
+  int (*parse_decoded_buffer) (const char *buf, int32_t size, MimeObject *obj);
+
+
+  /* Callbacks used by decryption module. */
+  void * (*crypto_init) (MimeObject *obj,
+             int (*output_fn) (const char *data, int32_t data_size,
+                       void *output_closure),
+             void *output_closure);
+  int (*crypto_write) (const char *data, int32_t data_size,
+             void *crypto_closure);
+  int (*crypto_eof) (void *crypto_closure, bool abort_p);
+  char * (*crypto_generate_html) (void *crypto_closure);
+  void (*crypto_free) (void *crypto_closure);
+};
+
+extern MimeEncryptedClass mimeEncryptedClass;
+
+struct MimeEncrypted {
+  MimeContainer container;     /* superclass variables */
+  void *crypto_closure;       /* Opaque data used by decryption module. */
+  MimeDecoderData *decoder_data; /* Opaque data for the Transfer-Encoding
+                  decoder. */
+  MimeHeaders *hdrs;       /* Headers of the enclosed object (including
+                  the type of the *decrypted* data.) */
+  MimePartBufferData *part_buffer;  /* The data of the decrypted enclosed
+                     object (see mimepbuf.h) */
+};
+
+#define MimeEncryptedClassInitializer(ITYPE,CSUPER) \
+  { MimeContainerClassInitializer(ITYPE,CSUPER) }
+
+#endif /* _MIMECRYP_H_ */