Add (back) OpenPGP-S2K

It was removed somewhere along the line in 1.11, with the logic
that it is a funky PGP-specific scheme and (quoting the commit
that removed it) "not really useful outside of a full PGP implementation".

This assumed that the PGP implementation would be in Botan itself, but
PGP is implemented in https://github.com/evpo/EncryptPad/ (which is
a PGP implementation using 1.10), and RNP (https://github.com/riboseinc/rnp)
would like to use it also.

This work was sponsored by Ribose Inc (@riboseinc).

1 files changed, 67 insertions, 0 deletions

diff --git a/src/lib/pbkdf/pgp_s2k/pgp_s2k.h b/src/lib/pbkdf/pgp_s2k/pgp_s2k.h
new file mode 100644
index 000000000..3d85ba306
--- /dev/null
+++ b/src/lib/pbkdf/pgp_s2k/pgp_s2k.h
@@ -0,0 +1,67 @@
+/*
+* OpenPGP PBKDF
+* (C) 1999-2007,2017 Jack Lloyd
+*
+* Distributed under the terms of the Botan license
+*/
+
+#ifndef BOTAN_OPENPGP_S2K_H__
+#define BOTAN_OPENPGP_S2K_H__
+
+#include <botan/pbkdf.h>
+#include <botan/hash.h>
+
+namespace Botan {
+
+/**
+* OpenPGP's S2K
+*
+* See RFC 4880 sections 3.7.1.1, 3.7.1.2, and 3.7.1.3
+* If the salt is empty and iterations == 1, "simple" S2K is used
+* If the salt is non-empty and iterations == 1, "salted" S2K is used
+* If the salt is non-empty and iterations > 1, "iterated" S2K is used
+*
+* If iterations == 0 and msec.count() > 0, "iterated" S2K is assumed,
+* and the number of iterations performed is returned.
+*
+* Note that unlike PBKDF2, OpenPGP S2K's "iterations" are defined as
+* the number of bytes hashed.
+*/
+class BOTAN_DLL OpenPGP_S2K final : public PBKDF
+   {
+   public:
+      /**
+      * @param hash_in the hash function to use
+      */
+      explicit OpenPGP_S2K(HashFunction* hash) : m_hash(hash) {}
+
+      std::string name() const override
+         {
+         return "OpenPGP-S2K(" + m_hash->name() + ")";
+         }
+
+      PBKDF* clone() const
+         {
+         return new OpenPGP_S2K(m_hash->clone());
+         }
+
+      size_t pbkdf(uint8_t output_buf[], size_t output_len,
+                   const std::string& passphrase,
+                   const uint8_t salt[], size_t salt_len,
+                   size_t iterations,
+                   std::chrono::milliseconds msec) const override;
+
+      /**
+      * RFC 4880 encodes the iteration count to a single-byte value
+      */
+      static uint8_t encode_count(size_t iterations);
+
+      static size_t decode_count(uint8_t encoded_iter);
+
+   private:
+      std::unique_ptr<HashFunction> m_hash;
+   };
+
+}
+
+#endif