diff --git a/library/x509write.c b/library/x509write.c
index 026afe6..cf68b02 100644
--- a/library/x509write.c
+++ b/library/x509write.c
@@ -30,24 +30,8 @@
 #include "polarssl/asn1write.h"
 #include "polarssl/x509write.h"
 #include "polarssl/x509.h"
-#if defined(POLARSSL_MD2_C)
-#include "polarssl/md2.h"
-#endif
-#if defined(POLARSSL_MD4_C)
-#include "polarssl/md4.h"
-#endif
-#if defined(POLARSSL_MD5_C)
-#include "polarssl/md5.h"
-#endif
-#if defined(POLARSSL_SHA1_C)
-#include "polarssl/sha1.h"
-#endif
-#if defined(POLARSSL_SHA2_C)
-#include "polarssl/sha2.h"
-#endif
-#if defined(POLARSSL_SHA4_C)
-#include "polarssl/sha4.h"
-#endif
+#include "polarssl/md.h"
+#include "polarssl/oid.h"
 
 int x509_write_pubkey_der( unsigned char *buf, size_t size, rsa_context *rsa )
 {
@@ -157,41 +141,7 @@
     return( len );
 }
 
-/*
- * Wrapper for x509 hashes.
- */
-static void x509_hash( const unsigned char *in, size_t len, int alg,
-                       unsigned char *out )
-{
-    switch( alg )
-    {
-#if defined(POLARSSL_MD2_C)
-        case SIG_RSA_MD2    :  md2( in, len, out ); break;
-#endif
-#if defined(POLARSSL_MD4_C)
-        case SIG_RSA_MD4    :  md4( in, len, out ); break;
-#endif
-#if defined(POLARSSL_MD5_C)
-        case SIG_RSA_MD5    :  md5( in, len, out ); break;
-#endif
-#if defined(POLARSSL_SHA1_C)
-        case SIG_RSA_SHA1   : sha1( in, len, out ); break;
-#endif
-#if defined(POLARSSL_SHA2_C)
-        case SIG_RSA_SHA224 : sha2( in, len, out, 1 ); break;
-        case SIG_RSA_SHA256 : sha2( in, len, out, 0 ); break;
-#endif
-#if defined(POLARSSL_SHA4_C)
-        case SIG_RSA_SHA384 : sha4( in, len, out, 1 ); break;
-        case SIG_RSA_SHA512 : sha4( in, len, out, 0 ); break;
-#endif
-        default:
-            memset( out, '\xFF', 64 );
-            break;
-    }
-}
-
-int x509_write_sig( unsigned char **p, unsigned char *start, char *oid,
+int x509_write_sig( unsigned char **p, unsigned char *start, const char *oid,
                     unsigned char *sig, size_t size )
 {
     int ret;
@@ -218,10 +168,10 @@
 }
 
 int x509_write_cert_req( unsigned char *buf, size_t size, rsa_context *rsa,
-                         x509_req_name *req_name, int hash_id )
+                         x509_req_name *req_name, md_type_t md_alg )
 {
     int ret;
-    char sig_oid[10];
+    const char *sig_oid;
     unsigned char *c, *c2;
     unsigned char hash[64];
     unsigned char sig[POLARSSL_MPI_MAX_SIZE];
@@ -272,15 +222,13 @@
     ASN1_CHK_ADD( len, asn1_write_len( &c, tmp_buf, len ) );
     ASN1_CHK_ADD( len, asn1_write_tag( &c, tmp_buf, ASN1_CONSTRUCTED | ASN1_SEQUENCE ) );
     
-    x509_hash( c, len, hash_id, hash );
+    md( md_info_from_type( md_alg ), c, len, hash );
 
-    rsa_pkcs1_sign( rsa, NULL, NULL, RSA_PRIVATE, hash_id, 0, hash, sig );
+    rsa_pkcs1_sign( rsa, NULL, NULL, RSA_PRIVATE, md_alg, 0, hash, sig );
 
     // Generate correct OID
     //
-    memcpy( sig_oid, OID_PKCS1, 8 );
-    sig_oid[8] = hash_id;
-    sig_oid[9] = '\0';
+    ret = oid_get_oid_by_sig_alg( POLARSSL_PK_RSA, md_alg, &sig_oid );
 
     c2 = buf + size - 1;
     ASN1_CHK_ADD( sig_len, x509_write_sig( &c2, buf, sig_oid, sig, rsa->len ) );