Added pk_decrypt, pk_encrypt, pk_sign, pk_verify example applications
diff --git a/programs/pkey/pk_sign.c b/programs/pkey/pk_sign.c
new file mode 100644
index 0000000..61a4868
--- /dev/null
+++ b/programs/pkey/pk_sign.c
@@ -0,0 +1,168 @@
+/*
+ *  Public key-based signature creation program
+ *
+ *  Copyright (C) 2006-2013, Brainspark B.V.
+ *
+ *  This file is part of PolarSSL (http://www.polarssl.org)
+ *  Lead Maintainer: Paul Bakker <polarssl_maintainer at polarssl.org>
+ *
+ *  All rights reserved.
+ *
+ *  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
+ *  (at your option) 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.
+ */
+
+#ifndef _CRT_SECURE_NO_DEPRECATE
+#define _CRT_SECURE_NO_DEPRECATE 1
+#endif
+
+#include <string.h>
+#include <stdio.h>
+
+#include "polarssl/config.h"
+
+#include "polarssl/error.h"
+#include "polarssl/entropy.h"
+#include "polarssl/ctr_drbg.h"
+#include "polarssl/md.h"
+#include "polarssl/pk.h"
+#include "polarssl/sha1.h"
+
+#if defined _MSC_VER && !defined snprintf
+#define snprintf _snprintf
+#endif
+
+#if !defined(POLARSSL_BIGNUM_C) || !defined(POLARSSL_ENTROPY_C) ||  \
+    !defined(POLARSSL_SHA1_C) ||                                    \
+    !defined(POLARSSL_PK_PARSE_C) || !defined(POLARSSL_FS_IO) ||    \
+    !defined(POLARSSL_CTR_DRBG_C)
+int main( int argc, char *argv[] )
+{
+    ((void) argc);
+    ((void) argv);
+
+    printf("POLARSSL_BIGNUM_C and/or POLARSSL_ENTROPY_C and/or "
+           "POLARSSL_SHA1_C and/or "
+           "POLARSSL_PK_PARSE_C and/or POLARSSL_FS_IO and/or "
+           "POLARSSL_CTR_DRBG_C not defined.\n");
+    return( 0 );
+}
+#else
+int main( int argc, char *argv[] )
+{
+    FILE *f;
+    int ret;
+    pk_context pk;
+    entropy_context entropy;
+    ctr_drbg_context ctr_drbg;
+    unsigned char hash[20];
+    unsigned char buf[POLARSSL_MPI_MAX_SIZE];
+    char filename[512];
+    const char *pers = "pk_sign";
+    size_t olen = 0;
+
+    ret = 1;
+
+    if( argc != 3 )
+    {
+        printf( "usage: pk_sign <key_file> <filename>\n" );
+
+#if defined(_WIN32)
+        printf( "\n" );
+#endif
+
+        goto exit;
+    }
+
+    printf( "\n  . Seeding the random number generator..." );
+    fflush( stdout );
+
+    entropy_init( &entropy );
+    if( ( ret = ctr_drbg_init( &ctr_drbg, entropy_func, &entropy,
+                               (const unsigned char *) pers,
+                               strlen( pers ) ) ) != 0 )
+    {
+        polarssl_strerror( ret, (char *) buf, sizeof(buf) );
+        printf( " failed\n  ! ctr_drbg_init returned -0x%04x - %s\n\n", -ret, buf );
+        goto exit;
+    }
+
+    printf( "\n  . Reading private key from '%s'", argv[1] );
+    fflush( stdout );
+
+    pk_init( &pk );
+
+    if( ( ret = pk_parse_keyfile( &pk, argv[1], "" ) ) != 0 )
+    {
+        ret = 1;
+        printf( " failed\n  ! Could not open '%s'\n", argv[1] );
+        goto exit;
+    }
+
+    /*
+     * Compute the SHA-1 hash of the input file,
+     * then calculate the signature of the hash.
+     */
+    printf( "\n  . Generating the SHA-1 signature" );
+    fflush( stdout );
+
+    if( ( ret = sha1_file( argv[2], hash ) ) != 0 )
+    {
+        printf( " failed\n  ! Could not open or read %s\n\n", argv[2] );
+        goto exit;
+    }
+
+    if( ( ret = pk_sign( &pk, POLARSSL_MD_SHA1, hash, 0, buf, &olen,
+                         ctr_drbg_random, &ctr_drbg ) ) != 0 )
+    {
+        polarssl_strerror( ret, (char *) buf, sizeof(buf) );
+        printf( " failed\n  ! pk_sign returned -0x%04x - %s\n\n", -ret, buf );
+        goto exit;
+    }
+
+    /*
+     * Write the signature into <filename>-sig.txt
+     */
+    snprintf( filename, sizeof(filename), "%s.sig", argv[2] );
+
+    if( ( f = fopen( filename, "wb+" ) ) == NULL )
+    {
+        ret = 1;
+        printf( " failed\n  ! Could not create %s\n\n", filename );
+        goto exit;
+    }
+
+    if( fwrite( buf, 1, olen, f ) != olen )
+    {
+        printf( "failed\n  ! fwrite failed\n\n" );
+        goto exit;
+    }
+
+    fclose( f );
+
+    printf( "\n  . Done (created \"%s\")\n\n", filename );
+
+exit:
+    pk_free( &pk );
+
+#if defined(_WIN32)
+    printf( "  + Press Enter to exit this program.\n" );
+    fflush( stdout ); getchar();
+#endif
+
+    return( ret );
+}
+#endif /* POLARSSL_BIGNUM_C && POLARSSL_ENTROPY_C &&
+          POLARSSL_SHA1_C && POLARSSL_PK_PARSE_C && POLARSSL_FS_IO &&
+          POLARSSL_CTR_DRBG_C */