diff --git a/include/polarssl/asn1write.h b/include/polarssl/asn1write.h
index 1eb7e69..d7f7b52 100644
--- a/include/polarssl/asn1write.h
+++ b/include/polarssl/asn1write.h
@@ -115,17 +115,19 @@
 /**
  * \brief           Write an AlgorithmIdentifier sequence in ASN.1 format
  *                  Note: function works backwards in data buffer
- *                  Note: Uses NULL as algorithm parameter
  *
  * \param p         reference to current position pointer
  * \param start     start of the buffer (for bounds-checking)
  * \param oid       the OID of the algorithm
  * \param oid_len   length of the OID
+ * \param par_len   length of parameters, which must be already written.
+ *                  If 0, NULL parameters are added
  *
  * \return          the length written or a negative error code
  */
 int asn1_write_algorithm_identifier( unsigned char **p, unsigned char *start,
-                                     const char *oid, size_t oid_len );
+                                     const char *oid, size_t oid_len,
+                                     size_t par_len );
 
 /**
  * \brief           Write a boolean tag (ASN1_BOOLEAN) and value in ASN.1 format
diff --git a/include/polarssl/oid.h b/include/polarssl/oid.h
index 6981237..ba0ce7d 100644
--- a/include/polarssl/oid.h
+++ b/include/polarssl/oid.h
@@ -370,6 +370,18 @@
  */
 int oid_get_pk_alg( const asn1_buf *oid, pk_type_t *pk_alg );
 
+/**
+ * \brief          Translate pk_type into PublicKeyAlgorithm OID
+ *
+ * \param pk_alg   Public key type to look for
+ * \param oid      place to store ASN.1 OID string pointer
+ * \param olen     length of the OID
+ *
+ * \return         0 if successful, or POLARSSL_ERR_OID_NOT_FOUND
+ */
+int oid_get_oid_by_pk_alg( pk_type_t pk_alg,
+                           const char **oid, size_t *olen );
+
 #if defined(POLARSSL_ECP_C)
 /**
  * \brief          Translate NamedCurve OID into an EC group identifier
@@ -382,9 +394,9 @@
 int oid_get_ec_grp( const asn1_buf *oid, ecp_group_id *grp_id );
 
 /**
- * \brief           Translate EC group identifier into NamedCurve OID
+ * \brief          Translate EC group identifier into NamedCurve OID
  *
- * \param grp_id    EC group identifier
+ * \param grp_id   EC group identifier
  * \param oid      place to store ASN.1 OID string pointer
  * \param olen     length of the OID
  *