Add a new interface CryptoBox which provides basic password-based encryption

in a reasonable way. Low on features, which is rather intentional. There
is a version code included in the format so further extensions are possible, if
warranted.

Inspired by the n-th mailing list request for such a class. Realized it was
probably better that I design such code than random people who just want
'something that works'.

1 files changed, 146 insertions, 0 deletions

diff --git a/src/cryptobox/cryptobox.cpp b/src/cryptobox/cryptobox.cpp
new file mode 100644
index 000000000..c27bbaffa
--- /dev/null
+++ b/src/cryptobox/cryptobox.cpp
@@ -0,0 +1,146 @@
+/*
+* Cryptobox Message Routines
+* (C) 2009 Jack Lloyd
+*
+* Distributed under the terms of the Botan license
+*/
+
+#include <botan/cryptobox.h>
+#include <botan/filters.h>
+#include <botan/pipe.h>
+#include <botan/serpent.h>
+#include <botan/sha2_64.h>
+#include <botan/ctr.h>
+#include <botan/hmac.h>
+#include <botan/pbkdf2.h>
+#include <botan/pem.h>
+#include <botan/loadstor.h>
+#include <botan/mem_ops.h>
+
+namespace Botan {
+
+namespace CryptoBox {
+
+namespace {
+
+/*
+First 24 bits of SHA-256("Botan Cryptobox"), followed by 8 0 bits
+for later use as flags, etc if needed
+*/
+const u32bit CRYPTOBOX_VERSION_CODE = 0xEFC22400;
+
+const u32bit VERSION_CODE_LEN = 4;
+const u32bit CIPHER_KEY_LEN = 32;
+const u32bit CIPHER_IV_LEN = 16;
+const u32bit MAC_KEY_LEN = 32;
+const u32bit MAC_OUTPUT_LEN = 20;
+const u32bit PBKDF_SALT_LEN = 10;
+const u32bit PBKDF_ITERATIONS = 8 * 1024;
+
+const u32bit PBKDF_OUTPUT_LEN = CIPHER_KEY_LEN + CIPHER_IV_LEN + MAC_KEY_LEN;
+
+}
+
+std::string encrypt(const byte input[], u32bit input_len,
+                    const std::string& passphrase,
+                    RandomNumberGenerator& rng)
+   {
+   SecureVector<byte> pbkdf_salt(PBKDF_SALT_LEN);
+   rng.randomize(pbkdf_salt.begin(), pbkdf_salt.size());
+
+   PKCS5_PBKDF2 pbkdf(new HMAC(new SHA_512));
+   pbkdf.change_salt(pbkdf_salt.begin(), pbkdf_salt.size());
+   pbkdf.set_iterations(PBKDF_ITERATIONS);
+
+   OctetString mk = pbkdf.derive_key(PBKDF_OUTPUT_LEN, passphrase);
+
+   SymmetricKey cipher_key(mk.begin(), CIPHER_KEY_LEN);
+   SymmetricKey mac_key(mk.begin() + CIPHER_KEY_LEN, MAC_KEY_LEN);
+   InitializationVector iv(mk.begin() + CIPHER_KEY_LEN + MAC_KEY_LEN,
+                           CIPHER_IV_LEN);
+
+   Pipe pipe(new CTR_BE(new Serpent, cipher_key, iv),
+             new Fork(
+                0,
+                new MAC_Filter(new HMAC(new SHA_512),
+                               mac_key, MAC_OUTPUT_LEN)));
+
+   pipe.process_msg(input, input_len);
+
+   /*
+   Output format is:
+      version # (4 bytes)
+      salt (10 bytes)
+      mac (20 bytes)
+      ciphertext
+   */
+   u32bit ciphertext_len = pipe.remaining(0);
+
+   SecureVector<byte> out_buf;
+
+   for(u32bit i = 0; i != VERSION_CODE_LEN; ++i)
+      out_buf.append(get_byte(i, CRYPTOBOX_VERSION_CODE));
+
+   out_buf.append(pbkdf_salt.begin(), pbkdf_salt.size());
+
+   out_buf.grow_to(out_buf.size() + MAC_OUTPUT_LEN + ciphertext_len);
+   pipe.read(out_buf + VERSION_CODE_LEN + PBKDF_SALT_LEN, MAC_OUTPUT_LEN, 1);
+   pipe.read(out_buf + VERSION_CODE_LEN + PBKDF_SALT_LEN + MAC_OUTPUT_LEN,
+             ciphertext_len, 0);
+
+   return PEM_Code::encode(out_buf.begin(), out_buf.size(),
+                           "BOTAN CRYPTOBOX MESSAGE");
+   }
+
+std::string decrypt(const byte input[], u32bit input_len,
+                    const std::string& passphrase)
+   {
+   DataSource_Memory input_src(input, input_len);
+   SecureVector<byte> ciphertext =
+      PEM_Code::decode_check_label(input_src,
+                                   "BOTAN CRYPTOBOX MESSAGE");
+
+   if(ciphertext.size() < (VERSION_CODE_LEN + PBKDF_SALT_LEN + MAC_OUTPUT_LEN))
+      throw Decoding_Error("Invalid CryptoBox input");
+
+   for(u32bit i = 0; i != VERSION_CODE_LEN; ++i)
+      if(ciphertext[i] != get_byte(i, CRYPTOBOX_VERSION_CODE))
+         throw Decoding_Error("Bad CryptoBox version");
+
+   SecureVector<byte> pbkdf_salt(ciphertext + VERSION_CODE_LEN, PBKDF_SALT_LEN);
+
+   PKCS5_PBKDF2 pbkdf(new HMAC(new SHA_512));
+   pbkdf.change_salt(pbkdf_salt.begin(), pbkdf_salt.size());
+   pbkdf.set_iterations(PBKDF_ITERATIONS);
+
+   OctetString mk = pbkdf.derive_key(PBKDF_OUTPUT_LEN, passphrase);
+
+   SymmetricKey cipher_key(mk.begin(), CIPHER_KEY_LEN);
+   SymmetricKey mac_key(mk.begin() + CIPHER_KEY_LEN, MAC_KEY_LEN);
+   InitializationVector iv(mk.begin() + CIPHER_KEY_LEN + MAC_KEY_LEN,
+                           CIPHER_IV_LEN);
+
+   Pipe pipe(new Fork(
+                new CTR_BE(new Serpent, cipher_key, iv),
+                new MAC_Filter(new HMAC(new SHA_512),
+                               mac_key, MAC_OUTPUT_LEN)));
+
+   const u32bit ciphertext_offset =
+      VERSION_CODE_LEN + PBKDF_SALT_LEN + MAC_OUTPUT_LEN;
+
+   pipe.process_msg(ciphertext + ciphertext_offset,
+                    ciphertext.size() - ciphertext_offset);
+
+   byte computed_mac[MAC_OUTPUT_LEN];
+   pipe.read(computed_mac, MAC_OUTPUT_LEN, 1);
+
+   if(!same_mem(computed_mac, ciphertext + VERSION_CODE_LEN + PBKDF_SALT_LEN,
+                MAC_OUTPUT_LEN))
+      throw Integrity_Failure("CryptoBox integrity failure");
+
+   return pipe.read_all_as_string(0);
+   }
+
+}
+
+}