Add an example of reading SSH2 public keys

1 files changed, 119 insertions, 0 deletions

diff --git a/doc/examples/read_ssh.cpp b/doc/examples/read_ssh.cpp
new file mode 100644
index 000000000..a88306caa
--- /dev/null
+++ b/doc/examples/read_ssh.cpp
@@ -0,0 +1,119 @@
+/*
+* Example of reading SSH2 format public keys (see RFC 4716)
+*/
+
+#include <fstream>
+#include <botan/x509_key.h>
+#include <botan/filters.h>
+#include <botan/loadstor.h>
+#include <botan/rsa.h>
+#include <botan/dsa.h>
+
+using namespace Botan;
+
+u32bit read_u32bit(Pipe& pipe)
+   {
+   byte out[4] = { 0 };
+   pipe.read(out, 4);
+   u32bit len = load_be<u32bit>(out, 0);
+   if(len > 10000)
+      throw Decoding_Error("Huge size in read_u32bit, something went wrong");
+   return len;
+   }
+
+std::string read_string(Pipe& pipe)
+   {
+   u32bit len = read_u32bit(pipe);
+
+   std::string out(len, 'X');
+   pipe.read(reinterpret_cast<byte*>(&out[0]), len);
+   return out;
+   }
+
+BigInt read_bigint(Pipe& pipe)
+   {
+   u32bit len = read_u32bit(pipe);
+
+   SecureVector<byte> buf(len);
+   pipe.read(&buf[0], len);
+   return BigInt::decode(buf);
+   }
+
+Public_Key* read_ssh_pubkey(const std::string& file)
+   {
+   std::ifstream in(file.c_str());
+
+   const std::string ssh_header = "---- BEGIN SSH2 PUBLIC KEY ----";
+   const std::string ssh_trailer = "---- END SSH2 PUBLIC KEY ----";
+
+   std::string hex_bits;
+
+   std::string line;
+   std::getline(in, line);
+
+   if(line != ssh_header)
+      return 0;
+
+   while(in.good())
+      {
+      std::getline(in, line);
+
+      if(line.find("Comment: ") == 0)
+         {
+         while(line[line.size()-1] == '\\')
+            std::getline(in, line);
+         std::getline(in, line);
+         }
+
+      if(line == ssh_trailer)
+         break;
+
+      hex_bits += line;
+      }
+
+   Pipe pipe(new Base64_Decoder);
+   pipe.process_msg(hex_bits);
+
+   std::string key_type = read_string(pipe);
+
+   if(key_type != "ssh-rsa" && key_type != "ssh-dss")
+      return 0;
+
+   if(key_type == "ssh-rsa")
+      {
+      BigInt e = read_bigint(pipe);
+      BigInt n = read_bigint(pipe);
+      return new RSA_PublicKey(n, e);
+      }
+   else if(key_type == "ssh-dss")
+      {
+      BigInt p = read_bigint(pipe);
+      BigInt q = read_bigint(pipe);
+      BigInt g = read_bigint(pipe);
+      BigInt y = read_bigint(pipe);
+
+      return new DSA_PublicKey(DL_Group(p, q, g), y);
+      }
+
+   return 0;
+   }
+
+#include <botan/init.h>
+#include <iostream>
+
+int main()
+   {
+   LibraryInitializer init;
+
+   Public_Key* key = read_ssh_pubkey("dsa.ssh");
+
+   if(key == 0)
+      {
+      std::cout << "Failed\n";
+      return 1;
+      }
+
+   std::cout << X509::PEM_encode(*key);
+
+   return 0;
+   }