diff --git a/library/x509_crt_write.c b/library/x509_crt_write.c
new file mode 100644
index 0000000..577097d
--- /dev/null
+++ b/library/x509_crt_write.c
@@ -0,0 +1,426 @@
+/*
+ *  X.509 certificate writing
+ *
+ *  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.
+ */
+/*
+ * References:
+ * - certificates: RFC 5280, updated by RFC 6818
+ * - CSRs: PKCS#10 v1.7 aka RFC 2986
+ * - attributes: PKCS#9 v2.0 aka RFC 2985
+ */
+
+#include "polarssl/config.h"
+
+#if defined(POLARSSL_X509_CRT_WRITE_C)
+
+#include "polarssl/x509_crt.h"
+#include "polarssl/oid.h"
+#include "polarssl/asn1write.h"
+#include "polarssl/sha1.h"
+
+#if defined(POLARSSL_PEM_WRITE_C)
+#include "polarssl/pem.h"
+#endif /* POLARSSL_PEM_WRITE_C */
+
+void x509write_crt_init( x509write_cert *ctx )
+{
+    memset( ctx, 0, sizeof(x509write_cert) );
+
+    mpi_init( &ctx->serial );
+    ctx->version = X509_CRT_VERSION_3;
+}
+
+void x509write_crt_free( x509write_cert *ctx )
+{
+    mpi_free( &ctx->serial );
+
+    asn1_free_named_data_list( &ctx->subject );
+    asn1_free_named_data_list( &ctx->issuer );
+    asn1_free_named_data_list( &ctx->extensions );
+
+    memset( ctx, 0, sizeof(x509write_cert) );
+}
+
+void x509write_crt_set_md_alg( x509write_cert *ctx, md_type_t md_alg )
+{
+    ctx->md_alg = md_alg;
+}
+
+void x509write_crt_set_subject_key( x509write_cert *ctx, pk_context *key )
+{
+    ctx->subject_key = key;
+}
+
+void x509write_crt_set_issuer_key( x509write_cert *ctx, pk_context *key )
+{
+    ctx->issuer_key = key;
+}
+
+int x509write_crt_set_subject_name( x509write_cert *ctx, char *subject_name )
+{
+    return x509write_string_to_names( &ctx->subject, subject_name );
+}
+
+int x509write_crt_set_issuer_name( x509write_cert *ctx, char *issuer_name )
+{
+    return x509write_string_to_names( &ctx->issuer, issuer_name );
+}
+
+int x509write_crt_set_serial( x509write_cert *ctx, const mpi *serial )
+{
+    int ret;
+
+    if( ( ret = mpi_copy( &ctx->serial, serial ) ) != 0 )
+        return( ret );
+
+    return( 0 );
+}
+
+int x509write_crt_set_validity( x509write_cert *ctx, char *not_before,
+                                char *not_after )
+{
+    if( strlen(not_before) != X509_RFC5280_UTC_TIME_LEN - 1 ||
+        strlen(not_after)  != X509_RFC5280_UTC_TIME_LEN - 1 )
+    {
+        return( POLARSSL_ERR_X509WRITE_BAD_INPUT_DATA );
+    }
+    strncpy( ctx->not_before, not_before, X509_RFC5280_UTC_TIME_LEN );
+    strncpy( ctx->not_after , not_after , X509_RFC5280_UTC_TIME_LEN );
+    ctx->not_before[X509_RFC5280_UTC_TIME_LEN - 1] = 'Z';
+    ctx->not_after[X509_RFC5280_UTC_TIME_LEN - 1] = 'Z';
+
+    return( 0 );
+}
+
+int x509write_crt_set_extension( x509write_cert *ctx,
+                                 const char *oid, size_t oid_len,
+                                 int critical,
+                                 const unsigned char *val, size_t val_len )
+{
+    return x509_set_extension( &ctx->extensions, oid, oid_len,
+                               critical, val, val_len );
+}
+
+int x509write_crt_set_basic_constraints( x509write_cert *ctx,
+                                         int is_ca, int max_pathlen )
+{
+    int ret;
+    unsigned char buf[9];
+    unsigned char *c = buf + sizeof(buf);
+    size_t len = 0;
+
+    memset( buf, 0, sizeof(buf) );
+
+    if( is_ca && max_pathlen > 127 )
+        return( POLARSSL_ERR_X509WRITE_BAD_INPUT_DATA );
+
+    if( is_ca )
+    {
+        if( max_pathlen >= 0 )
+        {
+            ASN1_CHK_ADD( len, asn1_write_int( &c, buf, max_pathlen ) );
+        }
+        ASN1_CHK_ADD( len, asn1_write_bool( &c, buf, 1 ) );
+    }
+
+    ASN1_CHK_ADD( len, asn1_write_len( &c, buf, len ) );
+    ASN1_CHK_ADD( len, asn1_write_tag( &c, buf, ASN1_CONSTRUCTED | ASN1_SEQUENCE ) );
+
+    return x509write_crt_set_extension( ctx, OID_BASIC_CONSTRAINTS,
+                                        OID_SIZE( OID_BASIC_CONSTRAINTS ),
+                                        0, buf + sizeof(buf) - len, len );
+}
+
+int x509write_crt_set_subject_key_identifier( x509write_cert *ctx )
+{
+    int ret;
+    unsigned char buf[POLARSSL_MPI_MAX_SIZE * 2 + 20]; /* tag, length + 2xMPI */
+    unsigned char *c = buf + sizeof(buf);
+    size_t len = 0;
+
+    memset( buf, 0, sizeof(buf));
+    ASN1_CHK_ADD( len, pk_write_pubkey( &c, buf, ctx->subject_key ) );
+
+    sha1( buf + sizeof(buf) - len, len, buf + sizeof(buf) - 20 );
+    c = buf + sizeof(buf) - 20;
+    len = 20;
+
+    ASN1_CHK_ADD( len, asn1_write_len( &c, buf, len ) );
+    ASN1_CHK_ADD( len, asn1_write_tag( &c, buf, ASN1_OCTET_STRING ) );
+
+    return x509write_crt_set_extension( ctx, OID_SUBJECT_KEY_IDENTIFIER,
+                                        OID_SIZE( OID_SUBJECT_KEY_IDENTIFIER ),
+                                        0, buf + sizeof(buf) - len, len );
+}
+
+int x509write_crt_set_authority_key_identifier( x509write_cert *ctx )
+{
+    int ret;
+    unsigned char buf[POLARSSL_MPI_MAX_SIZE * 2 + 20]; /* tag, length + 2xMPI */
+    unsigned char *c = buf + sizeof(buf);
+    size_t len = 0;
+
+    memset( buf, 0, sizeof(buf));
+    ASN1_CHK_ADD( len, pk_write_pubkey( &c, buf, ctx->issuer_key ) );
+
+    sha1( buf + sizeof(buf) - len, len, buf + sizeof(buf) - 20 );
+    c = buf + sizeof(buf) - 20;
+    len = 20;
+
+    ASN1_CHK_ADD( len, asn1_write_len( &c, buf, len ) );
+    ASN1_CHK_ADD( len, asn1_write_tag( &c, buf, ASN1_CONTEXT_SPECIFIC | 0 ) );
+
+    ASN1_CHK_ADD( len, asn1_write_len( &c, buf, len ) );
+    ASN1_CHK_ADD( len, asn1_write_tag( &c, buf, ASN1_CONSTRUCTED | ASN1_SEQUENCE ) );
+
+    return x509write_crt_set_extension( ctx, OID_AUTHORITY_KEY_IDENTIFIER,
+                                   OID_SIZE( OID_AUTHORITY_KEY_IDENTIFIER ),
+                                   0, buf + sizeof(buf) - len, len );
+}
+
+int x509write_crt_set_key_usage( x509write_cert *ctx, unsigned char key_usage )
+{
+    unsigned char buf[4];
+    unsigned char *c;
+    int ret;
+
+    c = buf + 4;
+
+    if( ( ret = asn1_write_bitstring( &c, buf, &key_usage, 7 ) ) != 4 )
+        return( ret );
+
+    ret = x509write_crt_set_extension( ctx, OID_KEY_USAGE,
+                                       OID_SIZE( OID_KEY_USAGE ),
+                                       1, buf, 4 );
+    if( ret != 0 )
+        return( ret );
+
+    return( 0 );
+}
+
+int x509write_crt_set_ns_cert_type( x509write_cert *ctx,
+                                    unsigned char ns_cert_type )
+{
+    unsigned char buf[4];
+    unsigned char *c;
+    int ret;
+
+    c = buf + 4;
+
+    if( ( ret = asn1_write_bitstring( &c, buf, &ns_cert_type, 8 ) ) != 4 )
+        return( ret );
+
+    ret = x509write_crt_set_extension( ctx, OID_NS_CERT_TYPE,
+                                       OID_SIZE( OID_NS_CERT_TYPE ),
+                                       0, buf, 4 );
+    if( ret != 0 )
+        return( ret );
+
+    return( 0 );
+}
+
+static int x509_write_time( unsigned char **p, unsigned char *start,
+                            const char *time, size_t size )
+{
+    int ret;
+    size_t len = 0;
+
+    /*
+     * write ASN1_UTC_TIME if year < 2050 (2 bytes shorter)
+     */
+    if( time[0] == '2' && time[1] == '0' && time [2] < '5' )
+    {
+        ASN1_CHK_ADD( len, asn1_write_raw_buffer( p, start,
+                                             (const unsigned char *) time + 2,
+                                             size - 2 ) );
+        ASN1_CHK_ADD( len, asn1_write_len( p, start, len ) );
+        ASN1_CHK_ADD( len, asn1_write_tag( p, start, ASN1_UTC_TIME ) );
+    }
+    else
+    {
+        ASN1_CHK_ADD( len, asn1_write_raw_buffer( p, start,
+                                                  (const unsigned char *) time,
+                                                  size ) );
+        ASN1_CHK_ADD( len, asn1_write_len( p, start, len ) );
+        ASN1_CHK_ADD( len, asn1_write_tag( p, start, ASN1_GENERALIZED_TIME ) );
+    }
+
+    return( len );
+}
+
+int x509write_crt_der( x509write_cert *ctx, unsigned char *buf, size_t size,
+                       int (*f_rng)(void *, unsigned char *, size_t),
+                       void *p_rng )
+{
+    int ret;
+    const char *sig_oid;
+    size_t sig_oid_len = 0;
+    unsigned char *c, *c2;
+    unsigned char hash[64];
+    unsigned char sig[POLARSSL_MPI_MAX_SIZE];
+    unsigned char tmp_buf[2048];
+    size_t sub_len = 0, pub_len = 0, sig_and_oid_len = 0, sig_len;
+    size_t len = 0;
+    pk_type_t pk_alg;
+
+    /*
+     * Prepare data to be signed in tmp_buf
+     */
+    c = tmp_buf + sizeof( tmp_buf );
+
+    /* Signature algorithm needed in TBS, and later for actual signature */
+    pk_alg = pk_get_type( ctx->issuer_key );
+    if( pk_alg == POLARSSL_PK_ECKEY )
+        pk_alg = POLARSSL_PK_ECDSA;
+
+    if( ( ret = oid_get_oid_by_sig_alg( pk_alg, ctx->md_alg,
+                                        &sig_oid, &sig_oid_len ) ) != 0 )
+    {
+        return( ret );
+    }
+
+    /*
+     *  Extensions  ::=  SEQUENCE SIZE (1..MAX) OF Extension
+     */
+    ASN1_CHK_ADD( len, x509_write_extensions( &c, tmp_buf, ctx->extensions ) );
+    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 ) );
+    ASN1_CHK_ADD( len, asn1_write_len( &c, tmp_buf, len ) );
+    ASN1_CHK_ADD( len, asn1_write_tag( &c, tmp_buf, ASN1_CONTEXT_SPECIFIC | ASN1_CONSTRUCTED | 3 ) );
+
+    /*
+     *  SubjectPublicKeyInfo
+     */
+    ASN1_CHK_ADD( pub_len, pk_write_pubkey_der( ctx->subject_key,
+                                                tmp_buf, c - tmp_buf ) );
+    c -= pub_len;
+    len += pub_len;
+
+    /*
+     *  Subject  ::=  Name
+     */
+    ASN1_CHK_ADD( len, x509_write_names( &c, tmp_buf, ctx->subject ) );
+
+    /*
+     *  Validity ::= SEQUENCE {
+     *       notBefore      Time,
+     *       notAfter       Time }
+     */
+    sub_len = 0;
+
+    ASN1_CHK_ADD( sub_len, x509_write_time( &c, tmp_buf, ctx->not_after,
+                                            X509_RFC5280_UTC_TIME_LEN ) );
+
+    ASN1_CHK_ADD( sub_len, x509_write_time( &c, tmp_buf, ctx->not_before,
+                                            X509_RFC5280_UTC_TIME_LEN ) );
+
+    len += sub_len;
+    ASN1_CHK_ADD( len, asn1_write_len( &c, tmp_buf, sub_len ) );
+    ASN1_CHK_ADD( len, asn1_write_tag( &c, tmp_buf, ASN1_CONSTRUCTED | ASN1_SEQUENCE ) );
+
+    /*
+     *  Issuer  ::=  Name
+     */
+    ASN1_CHK_ADD( len, x509_write_names( &c, tmp_buf, ctx->issuer ) );
+
+    /*
+     *  Signature   ::=  AlgorithmIdentifier
+     */
+    ASN1_CHK_ADD( len, asn1_write_algorithm_identifier( &c, tmp_buf,
+                       sig_oid, strlen( sig_oid ), 0 ) );
+
+    /*
+     *  Serial   ::=  INTEGER
+     */
+    ASN1_CHK_ADD( len, asn1_write_mpi( &c, tmp_buf, &ctx->serial ) );
+
+    /*
+     *  Version  ::=  INTEGER  {  v1(0), v2(1), v3(2)  }
+     */
+    sub_len = 0;
+    ASN1_CHK_ADD( sub_len, asn1_write_int( &c, tmp_buf, ctx->version ) );
+    len += sub_len;
+    ASN1_CHK_ADD( len, asn1_write_len( &c, tmp_buf, sub_len ) );
+    ASN1_CHK_ADD( len, asn1_write_tag( &c, tmp_buf, ASN1_CONTEXT_SPECIFIC | ASN1_CONSTRUCTED | 0 ) );
+
+    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 ) );
+
+    /*
+     * Make signature
+     */
+    md( md_info_from_type( ctx->md_alg ), c, len, hash );
+
+    if( ( ret = pk_sign( ctx->issuer_key, ctx->md_alg, hash, 0, sig, &sig_len,
+                         f_rng, p_rng ) ) != 0 )
+    {
+        return( ret );
+    }
+
+    /*
+     * Write data to output buffer
+     */
+    c2 = buf + size;
+    ASN1_CHK_ADD( sig_and_oid_len, x509_write_sig( &c2, buf,
+                                        sig_oid, sig_oid_len, sig, sig_len ) );
+
+    c2 -= len;
+    memcpy( c2, c, len );
+
+    len += sig_and_oid_len;
+    ASN1_CHK_ADD( len, asn1_write_len( &c2, buf, len ) );
+    ASN1_CHK_ADD( len, asn1_write_tag( &c2, buf, ASN1_CONSTRUCTED | ASN1_SEQUENCE ) );
+
+    return( len );
+}
+
+#define PEM_BEGIN_CRT           "-----BEGIN CERTIFICATE-----\n"
+#define PEM_END_CRT             "-----END CERTIFICATE-----\n"
+
+#if defined(POLARSSL_PEM_WRITE_C)
+int x509write_crt_pem( x509write_cert *crt, unsigned char *buf, size_t size,
+                       int (*f_rng)(void *, unsigned char *, size_t),
+                       void *p_rng )
+{
+    int ret;
+    unsigned char output_buf[4096];
+    size_t olen = 0;
+
+    if( ( ret = x509write_crt_der( crt, output_buf, sizeof(output_buf),
+                                   f_rng, p_rng ) ) < 0 )
+    {
+        return( ret );
+    }
+
+    if( ( ret = pem_write_buffer( PEM_BEGIN_CRT, PEM_END_CRT,
+                                  output_buf + sizeof(output_buf) - ret,
+                                  ret, buf, size, &olen ) ) != 0 )
+    {
+        return( ret );
+    }
+
+    return( 0 );
+}
+#endif /* POLARSSL_PEM_WRITE_C */
+
+#endif /* POLARSSL_X509_CRT_WRITE_C */