diff --git a/include/polarssl/error.h b/include/polarssl/error.h
index a084243..728b29e 100644
--- a/include/polarssl/error.h
+++ b/include/polarssl/error.h
@@ -27,6 +27,8 @@
 #ifndef POLARSSL_ERROR_H
 #define POLARSSL_ERROR_H
 
+#include <string.h>
+
 /**
  * Error code layout.
  *
diff --git a/library/arc4.c b/library/arc4.c
index 07665ad..488ddf7 100644
--- a/library/arc4.c
+++ b/library/arc4.c
@@ -143,7 +143,7 @@
 
         memcpy( ibuf, arc4_test_pt[i], 8 );
 
-        arc4_setup( &ctx, (unsigned char *) arc4_test_key[i], 8 );
+        arc4_setup( &ctx, arc4_test_key[i], 8 );
         arc4_crypt( &ctx, 8, ibuf, obuf );
 
         if( memcmp( obuf, arc4_test_ct[i], 8 ) != 0 )
diff --git a/library/base64.c b/library/base64.c
index 8cd279c..06305bb 100644
--- a/library/base64.c
+++ b/library/base64.c
@@ -218,16 +218,17 @@
 int base64_self_test( int verbose )
 {
     size_t len;
-    unsigned char *src, buffer[128];
+    const unsigned char *src;
+    unsigned char buffer[128];
 
     if( verbose != 0 )
         printf( "  Base64 encoding test: " );
 
     len = sizeof( buffer );
-    src = (unsigned char *) base64_test_dec;
+    src = base64_test_dec;
 
     if( base64_encode( buffer, &len, src, 64 ) != 0 ||
-         memcmp( base64_test_enc, buffer, 88 ) != 0 ) 
+         memcmp( base64_test_enc, buffer, 88 ) != 0 )
     {
         if( verbose != 0 )
             printf( "failed\n" );
@@ -239,7 +240,7 @@
         printf( "passed\n  Base64 decoding test: " );
 
     len = sizeof( buffer );
-    src = (unsigned char *) base64_test_enc;
+    src = base64_test_enc;
 
     if( base64_decode( buffer, &len, src, 88 ) != 0 ||
          memcmp( base64_test_dec, buffer, 64 ) != 0 )
diff --git a/library/des.c b/library/des.c
index 338d273..8ae5894 100644
--- a/library/des.c
+++ b/library/des.c
@@ -838,27 +838,27 @@
         switch( i )
         {
         case 0:
-            des_setkey_dec( &ctx, (unsigned char *) des3_test_keys );
+            des_setkey_dec( &ctx, des3_test_keys );
             break;
 
         case 1:
-            des_setkey_enc( &ctx, (unsigned char *) des3_test_keys );
+            des_setkey_enc( &ctx, des3_test_keys );
             break;
 
         case 2:
-            des3_set2key_dec( &ctx3, (unsigned char *) des3_test_keys );
+            des3_set2key_dec( &ctx3, des3_test_keys );
             break;
 
         case 3:
-            des3_set2key_enc( &ctx3, (unsigned char *) des3_test_keys );
+            des3_set2key_enc( &ctx3, des3_test_keys );
             break;
 
         case 4:
-            des3_set3key_dec( &ctx3, (unsigned char *) des3_test_keys );
+            des3_set3key_dec( &ctx3, des3_test_keys );
             break;
 
         case 5:
-            des3_set3key_enc( &ctx3, (unsigned char *) des3_test_keys );
+            des3_set3key_enc( &ctx3, des3_test_keys );
             break;
 
         default:
@@ -911,27 +911,27 @@
         switch( i )
         {
         case 0:
-            des_setkey_dec( &ctx, (unsigned char *) des3_test_keys );
+            des_setkey_dec( &ctx, des3_test_keys );
             break;
 
         case 1:
-            des_setkey_enc( &ctx, (unsigned char *) des3_test_keys );
+            des_setkey_enc( &ctx, des3_test_keys );
             break;
 
         case 2:
-            des3_set2key_dec( &ctx3, (unsigned char *) des3_test_keys );
+            des3_set2key_dec( &ctx3, des3_test_keys );
             break;
 
         case 3:
-            des3_set2key_enc( &ctx3, (unsigned char *) des3_test_keys );
+            des3_set2key_enc( &ctx3, des3_test_keys );
             break;
 
         case 4:
-            des3_set3key_dec( &ctx3, (unsigned char *) des3_test_keys );
+            des3_set3key_dec( &ctx3, des3_test_keys );
             break;
 
         case 5:
-            des3_set3key_enc( &ctx3, (unsigned char *) des3_test_keys );
+            des3_set3key_enc( &ctx3, des3_test_keys );
             break;
 
         default:
diff --git a/library/error.c b/library/error.c
index 7f13067..32d9cf1 100644
--- a/library/error.c
+++ b/library/error.c
@@ -27,6 +27,8 @@
 
 #if defined(POLARSSL_ERROR_C)
 
+#include "polarssl/error.h"
+
 #if defined(POLARSSL_AES_C)
 #include "polarssl/aes.h"
 #endif
diff --git a/library/md5.c b/library/md5.c
index b2ee10b..3097aeb 100644
--- a/library/md5.c
+++ b/library/md5.c
@@ -220,8 +220,7 @@
 
     if( left && ilen >= fill )
     {
-        memcpy( (void *) (ctx->buffer + left),
-                (void *) input, fill );
+        memcpy( (void *) (ctx->buffer + left), input, fill );
         md5_process( ctx, ctx->buffer );
         input += fill;
         ilen  -= fill;
@@ -237,8 +236,7 @@
 
     if( ilen > 0 )
     {
-        memcpy( (void *) (ctx->buffer + left),
-                (void *) input, ilen );
+        memcpy( (void *) (ctx->buffer + left), input, ilen );
     }
 }
 
@@ -269,7 +267,7 @@
     last = ctx->total[0] & 0x3F;
     padn = ( last < 56 ) ? ( 56 - last ) : ( 120 - last );
 
-    md5_update( ctx, (unsigned char *) md5_padding, padn );
+    md5_update( ctx, md5_padding, padn );
     md5_update( ctx, msglen, 8 );
 
     PUT_UINT32_LE( ctx->state[0], output,  0 );
diff --git a/library/pem.c b/library/pem.c
index 33e74ab..7070681 100644
--- a/library/pem.c
+++ b/library/pem.c
@@ -195,12 +195,12 @@
     if( ctx == NULL )
         return( POLARSSL_ERR_PEM_INVALID_DATA );
 
-    s1 = (unsigned char *) strstr( (char *) data, header );
+    s1 = (unsigned char *) strstr( (const char *) data, header );
 
     if( s1 == NULL )
         return( POLARSSL_ERR_PEM_NO_HEADER_PRESENT );
 
-    s2 = (unsigned char *) strstr( (char *) data, footer );
+    s2 = (unsigned char *) strstr( (const char *) data, footer );
 
     if( s2 == NULL || s2 <= s1 )
         return( POLARSSL_ERR_PEM_INVALID_DATA );
diff --git a/library/sha1.c b/library/sha1.c
index 1e82580..372c0c1 100644
--- a/library/sha1.c
+++ b/library/sha1.c
@@ -254,8 +254,7 @@
 
     if( left && ilen >= fill )
     {
-        memcpy( (void *) (ctx->buffer + left),
-                (void *) input, fill );
+        memcpy( (void *) (ctx->buffer + left), input, fill );
         sha1_process( ctx, ctx->buffer );
         input += fill;
         ilen  -= fill;
@@ -270,10 +269,7 @@
     }
 
     if( ilen > 0 )
-    {
-        memcpy( (void *) (ctx->buffer + left),
-                (void *) input, ilen );
-    }
+        memcpy( (void *) (ctx->buffer + left), input, ilen );
 }
 
 static const unsigned char sha1_padding[64] =
@@ -303,7 +299,7 @@
     last = ctx->total[0] & 0x3F;
     padn = ( last < 56 ) ? ( 56 - last ) : ( 120 - last );
 
-    sha1_update( ctx, (unsigned char *) sha1_padding, padn );
+    sha1_update( ctx, sha1_padding, padn );
     sha1_update( ctx, msglen, 8 );
 
     PUT_UINT32_BE( ctx->state[0], output,  0 );
diff --git a/library/sha2.c b/library/sha2.c
index af3a6ee..7b375ff 100644
--- a/library/sha2.c
+++ b/library/sha2.c
@@ -250,8 +250,7 @@
 
     if( left && ilen >= fill )
     {
-        memcpy( (void *) (ctx->buffer + left),
-                (void *) input, fill );
+        memcpy( (void *) (ctx->buffer + left), input, fill );
         sha2_process( ctx, ctx->buffer );
         input += fill;
         ilen  -= fill;
@@ -266,10 +265,7 @@
     }
 
     if( ilen > 0 )
-    {
-        memcpy( (void *) (ctx->buffer + left),
-                (void *) input, ilen );
-    }
+        memcpy( (void *) (ctx->buffer + left), input, ilen );
 }
 
 static const unsigned char sha2_padding[64] =
@@ -299,7 +295,7 @@
     last = ctx->total[0] & 0x3F;
     padn = ( last < 56 ) ? ( 56 - last ) : ( 120 - last );
 
-    sha2_update( ctx, (unsigned char *) sha2_padding, padn );
+    sha2_update( ctx, sha2_padding, padn );
     sha2_update( ctx, msglen, 8 );
 
     PUT_UINT32_BE( ctx->state[0], output,  0 );
diff --git a/library/sha4.c b/library/sha4.c
index 556cc4f..ca3fc90 100644
--- a/library/sha4.c
+++ b/library/sha4.c
@@ -242,8 +242,7 @@
 
     if( left && ilen >= fill )
     {
-        memcpy( (void *) (ctx->buffer + left),
-                (void *) input, fill );
+        memcpy( (void *) (ctx->buffer + left), input, fill );
         sha4_process( ctx, ctx->buffer );
         input += fill;
         ilen  -= fill;
@@ -258,10 +257,7 @@
     }
 
     if( ilen > 0 )
-    {
-        memcpy( (void *) (ctx->buffer + left),
-                (void *) input, ilen );
-    }
+        memcpy( (void *) (ctx->buffer + left), input, ilen );
 }
 
 static const unsigned char sha4_padding[128] =
@@ -295,7 +291,7 @@
     last = (size_t)( ctx->total[0] & 0x7F );
     padn = ( last < 112 ) ? ( 112 - last ) : ( 240 - last );
 
-    sha4_update( ctx, (unsigned char *) sha4_padding, padn );
+    sha4_update( ctx, sha4_padding, padn );
     sha4_update( ctx, msglen, 16 );
 
     PUT_UINT64_BE( ctx->state[0], output,  0 );
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index c6734d7..8d68eb6 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -2264,7 +2264,7 @@
 static void ssl_calc_finished_ssl(
                 ssl_context *ssl, unsigned char *buf, int from )
 {
-    char *sender;
+    const char *sender;
     md5_context  md5;
     sha1_context sha1;
 
@@ -2296,17 +2296,17 @@
     SSL_DEBUG_BUF( 4, "finished sha1 state", (unsigned char *)
                    sha1.state, sizeof( sha1.state ) );
 
-    sender = ( from == SSL_IS_CLIENT ) ? (char *) "CLNT"
-                                       : (char *) "SRVR";
+    sender = ( from == SSL_IS_CLIENT ) ? "CLNT"
+                                       : "SRVR";
 
     memset( padbuf, 0x36, 48 );
 
-    md5_update( &md5, (unsigned char *) sender, 4 );
+    md5_update( &md5, (const unsigned char *) sender, 4 );
     md5_update( &md5, session->master, 48 );
     md5_update( &md5, padbuf, 48 );
     md5_finish( &md5, md5sum );
 
-    sha1_update( &sha1, (unsigned char *) sender, 4 );
+    sha1_update( &sha1, (const unsigned char *) sender, 4 );
     sha1_update( &sha1, session->master, 48 );
     sha1_update( &sha1, padbuf, 40 );
     sha1_finish( &sha1, sha1sum );
@@ -2341,7 +2341,7 @@
                 ssl_context *ssl, unsigned char *buf, int from )
 {
     int len = 12;
-    char *sender;
+    const char *sender;
     md5_context  md5;
     sha1_context sha1;
     unsigned char padbuf[36];
@@ -2368,13 +2368,13 @@
                    sha1.state, sizeof( sha1.state ) );
 
     sender = ( from == SSL_IS_CLIENT )
-             ? (char *) "client finished"
-             : (char *) "server finished";
+             ? "client finished"
+             : "server finished";
 
     md5_finish(  &md5, padbuf );
     sha1_finish( &sha1, padbuf + 16 );
 
-    ssl->handshake->tls_prf( session->master, 48, sender,
+    ssl->handshake->tls_prf( session->master, 48, (char *) sender,
                              padbuf, 36, buf, len );
 
     SSL_DEBUG_BUF( 3, "calc finished result", buf, len );
@@ -2391,7 +2391,7 @@
                 ssl_context *ssl, unsigned char *buf, int from )
 {
     int len = 12;
-    char *sender;
+    const char *sender;
     sha2_context sha2;
     unsigned char padbuf[32];
 
@@ -2413,12 +2413,12 @@
                    sha2.state, sizeof( sha2.state ) );
 
     sender = ( from == SSL_IS_CLIENT )
-             ? (char *) "client finished"
-             : (char *) "server finished";
+             ? "client finished"
+             : "server finished";
 
     sha2_finish( &sha2, padbuf );
 
-    ssl->handshake->tls_prf( session->master, 48, sender,
+    ssl->handshake->tls_prf( session->master, 48, (char *) sender,
                              padbuf, 32, buf, len );
 
     SSL_DEBUG_BUF( 3, "calc finished result", buf, len );
@@ -2435,7 +2435,7 @@
                 ssl_context *ssl, unsigned char *buf, int from )
 {
     int len = 12;
-    char *sender;
+    const char *sender;
     sha4_context sha4;
     unsigned char padbuf[48];
 
@@ -2457,12 +2457,12 @@
                    sha4.state, sizeof( sha4.state ) );
 
     sender = ( from == SSL_IS_CLIENT )
-             ? (char *) "client finished"
-             : (char *) "server finished";
+             ? "client finished"
+             : "server finished";
 
     sha4_finish( &sha4, padbuf );
 
-    ssl->handshake->tls_prf( session->master, 48, sender,
+    ssl->handshake->tls_prf( session->master, 48, (char *) sender,
                              padbuf, 48, buf, len );
 
     SSL_DEBUG_BUF( 3, "calc finished result", buf, len );
@@ -3039,7 +3039,7 @@
     if( ssl->hostname == NULL )
         return( POLARSSL_ERR_SSL_MALLOC_FAILED );
 
-    memcpy( ssl->hostname, (unsigned char *) hostname,
+    memcpy( ssl->hostname, (const unsigned char *) hostname,
             ssl->hostname_len );
 
     ssl->hostname[ssl->hostname_len] = '\0';
diff --git a/library/x509parse.c b/library/x509parse.c
index 3ddfb14..686d9d1 100644
--- a/library/x509parse.c
+++ b/library/x509parse.c
@@ -1400,7 +1400,7 @@
      * one or more PEM certificates.
      */
 #if defined(POLARSSL_PEM_C)
-    if( strstr( (char *) buf, "-----BEGIN CERTIFICATE-----" ) != NULL )
+    if( strstr( (const char *) buf, "-----BEGIN CERTIFICATE-----" ) != NULL )
         buf_format = X509_FORMAT_PEM;
 #endif
 
@@ -3402,7 +3402,7 @@
 
     memset( &clicert, 0, sizeof( x509_cert ) );
 
-    ret = x509parse_crt( &clicert, (unsigned char *) test_cli_crt,
+    ret = x509parse_crt( &clicert, (const unsigned char *) test_cli_crt,
                          strlen( test_cli_crt ) );
     if( ret != 0 )
     {
@@ -3414,7 +3414,7 @@
 
     memset( &cacert, 0, sizeof( x509_cert ) );
 
-    ret = x509parse_crt( &cacert, (unsigned char *) test_ca_crt,
+    ret = x509parse_crt( &cacert, (const unsigned char *) test_ca_crt,
                          strlen( test_ca_crt ) );
     if( ret != 0 )
     {
@@ -3433,8 +3433,8 @@
     rsa_init( &rsa, RSA_PKCS_V15, 0 );
 
     if( ( ret = x509parse_key( &rsa,
-                    (unsigned char *) test_ca_key, i,
-                    (unsigned char *) test_ca_pwd, j ) ) != 0 )
+                    (const unsigned char *) test_ca_key, i,
+                    (const unsigned char *) test_ca_pwd, j ) ) != 0 )
     {
         if( verbose != 0 )
             printf( "failed\n" );
@@ -3462,7 +3462,7 @@
     i = strlen( test_dhm_params );
     j = strlen( test_ca_pwd );
 
-    if( ( ret = x509parse_dhm( &dhm, (unsigned char *) test_dhm_params, i ) ) != 0 )
+    if( ( ret = x509parse_dhm( &dhm, (const unsigned char *) test_dhm_params, i ) ) != 0 )
     {
         if( verbose != 0 )
             printf( "failed\n" );