diff --git a/include/polarssl/asn1write.h b/include/polarssl/asn1write.h
index 9b98afe..43408e2 100644
--- a/include/polarssl/asn1write.h
+++ b/include/polarssl/asn1write.h
@@ -35,23 +35,162 @@
 extern "C" {
 #endif
 
+/**
+ * \brief           Write a length field in ASN.1 format
+ *                  Note: function works backwards in data buffer
+ *
+ * \param p         reference to current position pointer
+ * \param start     start of the buffer (for bounds-checking)
+ * \param len       the length to write
+ *
+ * \return          the length written or a negative error code
+ */
 int asn1_write_len( unsigned char **p, unsigned char *start, size_t len );
+
+/**
+ * \brief           Write a ASN.1 tag in ASN.1 format
+ *                  Note: function works backwards in data buffer
+ *
+ * \param p         reference to current position pointer
+ * \param start     start of the buffer (for bounds-checking)
+ * \param tag       the tag to write
+ *
+ * \return          the length written or a negative error code
+ */
 int asn1_write_tag( unsigned char **p, unsigned char *start, unsigned char tag );
+
 #if defined(POLARSSL_BIGNUM_C)
+/**
+ * \brief           Write a big number (ASN1_INTEGER) in ASN.1 format
+ *                  Note: function works backwards in data buffer
+ *
+ * \param p         reference to current position pointer
+ * \param start     start of the buffer (for bounds-checking)
+ * \param X         the MPI to write
+ *
+ * \return          the length written or a negative error code
+ */
 int asn1_write_mpi( unsigned char **p, unsigned char *start, mpi *X );
 #endif
+
+/**
+ * \brief           Write a NULL tag (ASN1_NULL) with zero data in ASN.1 format
+ *                  Note: function works backwards in data buffer
+ *
+ * \param p         reference to current position pointer
+ * \param start     start of the buffer (for bounds-checking)
+ *
+ * \return          the length written or a negative error code
+ */
 int asn1_write_null( unsigned char **p, unsigned char *start );
+
+/**
+ * \brief           Write an OID tag (ASN1_OID) and data in ASN.1 format
+ *                  Note: function works backwards in data buffer
+ *
+ * \param p         reference to current position pointer
+ * \param start     start of the buffer (for bounds-checking)
+ * \param oid       the OID to write
+ *
+ * \return          the length written or a negative error code
+ */
 int asn1_write_oid( unsigned char **p, unsigned char *start, const char *oid );
-int asn1_write_algorithm_identifier( unsigned char **p, unsigned char *start, const char *algorithm_oid );
+
+/**
+ * \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
+ *
+ * \return          the length written or a negative error code
+ */
+int asn1_write_algorithm_identifier( unsigned char **p, unsigned char *start,
+                                     const char *oid );
+
+/**
+ * \brief           Write an int tag (ASN1_INTEGER) and value in ASN.1 format
+ *                  Note: function works backwards in data buffer
+ *
+ * \param p         reference to current position pointer
+ * \param start     start of the buffer (for bounds-checking)
+ * \param val       the integer value
+ *
+ * \return          the length written or a negative error code
+ */
 int asn1_write_int( unsigned char **p, unsigned char *start, int val );
+
+/**
+ * \brief           Write a printable string tag (ASN1_PRINTABLE_STRING) and
+ *                  value in ASN.1 format
+ *                  Note: function works backwards in data buffer
+ *
+ * \param p         reference to current position pointer
+ * \param start     start of the buffer (for bounds-checking)
+ * \param text      the text to write
+ *
+ * \return          the length written or a negative error code
+ */
 int asn1_write_printable_string( unsigned char **p, unsigned char *start,
                                  char *text );
+
+/**
+ * \brief           Write an IA5 string tag (ASN1_IA5_STRING) and
+ *                  value in ASN.1 format
+ *                  Note: function works backwards in data buffer
+ *
+ * \param p         reference to current position pointer
+ * \param start     start of the buffer (for bounds-checking)
+ * \param text      the text to write
+ *
+ * \return          the length written or a negative error code
+ */
 int asn1_write_ia5_string( unsigned char **p, unsigned char *start,
                                  char *text );
+
+/**
+ * \brief           Write a bitstring tag (ASN1_BIT_STRING) and
+ *                  value in ASN.1 format
+ *                  Note: function works backwards in data buffer
+ *
+ * \param p         reference to current position pointer
+ * \param start     start of the buffer (for bounds-checking)
+ * \param buf       the bitstring
+ * \param bits      the total number of bits in the bitstring
+ *
+ * \return          the length written or a negative error code
+ */
 int asn1_write_bitstring( unsigned char **p, unsigned char *start,
                           const unsigned char *buf, size_t bits );
+
+/**
+ * \brief           Write an octet string tag (ASN1_OCTET_STRING) and
+ *                  value in ASN.1 format
+ *                  Note: function works backwards in data buffer
+ *
+ * \param p         reference to current position pointer
+ * \param start     start of the buffer (for bounds-checking)
+ * \param buf       data buffer to write
+ * \param size      length of the data buffer
+ *
+ * \return          the length written or a negative error code
+ */
 int asn1_write_octet_string( unsigned char **p, unsigned char *start,
                              const unsigned char *buf, size_t size );
+
+/**
+ * \brief           Write raw buffer data
+ *                  Note: function works backwards in data buffer
+ *
+ * \param p         reference to current position pointer
+ * \param start     start of the buffer (for bounds-checking)
+ * \param buf       data buffer to write
+ * \param size      length of the data buffer
+ *
+ * \return          the length written or a negative error code
+ */
 int asn1_write_raw_buffer( unsigned char **p, unsigned char *start,
                            const unsigned char *buf, size_t size );
 
diff --git a/library/asn1write.c b/library/asn1write.c
index f08e105..07a3fbb 100644
--- a/library/asn1write.c
+++ b/library/asn1write.c
@@ -142,7 +142,7 @@
 }
 
 int asn1_write_algorithm_identifier( unsigned char **p, unsigned char *start,
-                                     const char *algorithm_oid )
+                                     const char *oid )
 {
     int ret;
     size_t null_len = 0;
@@ -155,7 +155,7 @@
 
     // Write OID
     //
-    ASN1_CHK_ADD( oid_len, asn1_write_oid( p, start, algorithm_oid ) );
+    ASN1_CHK_ADD( oid_len, asn1_write_oid( p, start, oid ) );
 
     len = oid_len + null_len;
     ASN1_CHK_ADD( len, asn1_write_len( p, start, oid_len + null_len ) );