RFC 2537 (rfc2537) - Page 2 of 6

RSA/MD5 KEYs and SIGs in the Domain Name System (DNS)

RFC 2537            RSA/MD5 KEYs and SIGs in the DNS          March 1999


   This document describes how to store RSA keys and and RSA/MD5 based
   signatures in the DNS.  Familiarity with the RSA algorithm is assumed
   [Schneier].  Implementation of the RSA algorithm in DNS is
   recommended.

   The key words "MUST", "REQUIRED", "SHOULD", "RECOMMENDED", and "MAY"
   in this document are to be interpreted as described in RFC 2119.

2. RSA Public KEY Resource Records

   RSA public keys are stored in the DNS as KEY RRs using algorithm
   number 1 [RFC 2535].  The structure of the algorithm specific portion
   of the RDATA part of such RRs is as shown below.

           Field             Size
           -----             ----
           exponent length   1 or 3 octets (see text)
           exponent          as specified by length field
           modulus           remaining space

   For interoperability, the exponent and modulus are each currently
   limited to 4096 bits in length.  The public key exponent is a
   variable length unsigned integer.  Its length in octets is
   represented as one octet if it is in the range of 1 to 255 and by a
   zero octet followed by a two octet unsigned length if it is longer
   than 255 bytes.  The public key modulus field is a multiprecision
   unsigned integer.  The length of the modulus can be determined from
   the RDLENGTH and the preceding RDATA fields including the exponent.
   Leading zero octets are prohibited in the exponent and modulus.

3. RSA/MD5 SIG Resource Records

   The signature portion of the SIG RR RDATA area, when using the
   RSA/MD5 algorithm, is calculated as shown below.  The data signed is
   determined as specified in [RFC 2535].  See [RFC 2535] for fields in
   the SIG RR RDATA which precede the signature itself.


     hash = MD5 ( data )

     signature = ( 00 | 01 | FF* | 00 | prefix | hash ) ** e (mod n)










Eastlake                    Standards Track