TLS                                                      P. Wouters, Ed.
Internet-Draft                                                   Red Hat
Intended status: Standards Track                      H. Tschofenig, Ed.
Expires: April 25, August 19, 2013                          Nokia Siemens Networks
                                                              J. Gilmore

                                                               S. Weiler
                                                            SPARTA, Inc.
                                                              T. Kivinen
                                                        October 22, 2012
                                                       February 15, 2013

  Out-of-Band Public Key Validation for Transport Layer Security (TLS)


   This document specifies a new certificate type for exchanging raw
   public keys in Transport Layer Security (TLS) and Datagram Transport
   Layer Security (DTLS) for use with out-of-band public key validation.
   Currently, TLS authentication can only occur via X.509-based Public
   Key Infrastructure (PKI) or OpenPGP certificates.  By specifying a
   minimum resource for raw public key exchange, implementations can use
   alternative public key validation methods.

   One such alternative public key valiation method is offered by the
   DNS-Based Authentication of Named Entities (DANE) together with DNS
   Security.  Another alternative is to utilize pre-configured keys, as
   is the case with sensors and other embedded devices.  The usage of
   raw public keys, instead of X.509-based certificates, leads to a
   smaller code footprint.

   This document introduces the support for raw public keys in TLS.

Status of this Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on April 25, August 19, 2013.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  New TLS Extension  . . . . . . . . . . . . . . . . . . . . . .  4  5
   4.  TLS Handshake Extension  . . . . . . . . . . . . . . . . . . .  7  8
     4.1.  Client Hello . . . . . . . . . . . . . . . . . . . . . . .  7  8
     4.2.  Server Hello . . . . . . . . . . . . . . . . . . . . . . .  7  9
     4.3.  Certificate Request  . . . . . . . . . . . . . . . . . . .  8  9
     4.4.  Other Handshake Messages . . . . . . . . . . . . . . . . .  8  9
     4.5.  Client authentication  . . . . . . . . . . . . . . . . . .  8  9
   5.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . .  8 10
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11 12
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12 13
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12 13
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 14
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 13 14
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 13 14
   Appendix A.  Example Encoding  . . . . . . . . . . . . . . . . . . 15
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14 16

1.  Introduction

   Traditionally, TLS server public keys are obtained in PKIX containers
   in-band using the TLS handshake and validated using trust anchors
   based on a [PKIX] certification authority (CA).  This method can add
   a complicated trust relationship that is difficult to validate.
   Examples of such complexity can be seen in [Defeating-SSL].

   Alternative methods are available that allow a TLS client to obtain
   the TLS server public key:

   o  The TLS server public key is obtained from a DNSSEC secured
      resource records using DANE [RFC6698].

   o  The TLS server public key is obtained from a [PKIX] certificate
      chain from an Lightweight Directory Access Protocol (LDAP) [LDAP]

   o  The TLS client and server public key is provisioned into the
      operating system firmware image, and updated via software updates.

   Some smart objects use the UDP-based Constrained Application Protocol
   (CoAP) [I-D.ietf-core-coap] to interact with a Web server to upload
   sensor data at a regular intervals, such as temperature readings.
   CoAP [I-D.ietf-core-coap] can utilize DTLS for securing the client-
   to-server communication.  As part of the manufacturing process, the
   embeded device may be configured with the address and the public key
   of a dedicated CoAP server, as well as a public key for the client
   itself.  The usage of X.509-based PKIX certificates [PKIX] may not
   suit all smart object deployments and would therefore be an
   unneccesarry burden.

   The Transport Layer Security (TLS) Protocol Version 1.2 [RFC5246]
   provides a framework for extensions to TLS as well as guidelines for
   designing such extensions.  This document defines an extension registers a new value to
   the support IANA certificate types registry for the support of raw public

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

3.  New TLS Extension

   This section describes the changes to the TLS handshake message
   contents when raw public key certificates are to be used.  Figure 3 4
   illustrates the exchange of messages as described in the sub-sections
   below.  The client and the server exchange the newly defined
   certificate_type extension make use of two new TLS
   extensions, namely 'client_certificate_type' and
   'server_certificate_type', and an already available IANA TLS
   Certificate Type registry [TLS-Certificate-Types-Registry] to
   indicate their ability and desire to exchange raw public keys.  These
   raw public keys, in the form of a SubjectPublicKeyInfo structure, are
   then carried inside the
   certificate Certificate payload.  The Certificate and the
   SubjectPublicKeyInfo structure is shown in Figure 1.

   opaque ASN.1Cert<1..2^24-1>;

   struct {

                   // certificate type defined in this document.
           case RawPublicKey:
             opaque ASN.1_subjectPublicKeyInfo<1..2^24-1>;

                   // X.509 certificate defined in RFC 5246
           case X.509:
                     ASN.1Cert certificate_list<0..2^24-1>;

                   // Additional certificate type based on TLS
           // Certificate Type Registry
   } Certificate;

                   Figure 1: TLS Certificate Structure.

   The SubjectPublicKeyInfo structure is defined in Section 4.1 of RFC 5280.  Note that the SubjectPublicKeyInfo block
   5280 [PKIX] and does not only contain the raw keys, such as the
   public exponent and the modulus of an RSA public key, but also an
   algorithm identifier.  The structure, as shown in Figure 1, 2, is
   encoded in an ASN.1 format and therefore contains length information
   as well.  An example is provided in Appendix A.

      SubjectPublicKeyInfo  ::=  SEQUENCE  {
           algorithm            AlgorithmIdentifier,
           subjectPublicKey     BIT STRING  }

              Figure 1: 2: SubjectPublicKeyInfo ASN.1 Structure.

   The algorithm identifiers are Object Identifiers (OIDs).  RFC 3279
   [RFC3279], for example, defines the following OIDs shown in Figure 2. 3.

Key Type               | Document                   | OID
RSA                    | Section 2.3.1 of RFC 3279  | 1.2.840.113549.1.1
Digital Signature      |                            |
Algorithm (DSS)        | Section 2.3.2 of RFC 3279  | 1.2.840.10040.4.1
Elliptic Curve         |                            |
Digital Signature      |                            |
Algorithm (ECDSA)      | Section 2.3.5 of RFC 3279  | 1.2.840.10045.2.1

                 Figure 2: 3: Example Algorithm Identifiers.

   The message exchange in Figure 4 shows the 'client_certificate_type'
   and 'server_certificate_type' extensions added to the client and
   server hello messages.

    server_certificate_type   ->

                              <-  server_hello,
    finished                  ->

                              <- change_cipher_spec,

   Application Data        <------->     Application Data

               Figure 3: 4: Basic Raw Public Key TLS Exchange.

   The "certificate_type" TLS extension carries semantic of the two extensions is defined as follows:

      The 'client_certificate_type' and 'server_certificate_type' sent
      in the client hello, may carry a list of supported certificate types the client can send and receive,
      types, sorted by client preference.  Two values are defined for each certificate types to
   differentiate whether a client or a server  It is able to process a list in the case
      where the client supports multiple certificate of a specific type or can also send it.  This types.  These
      extension MUST be omitted if the client only supports X.509
      certificates.  The
   "extension_data" field of this extension contains a CertTypeExtension

   Note that the CertTypeExtension structure is being used both by 'client_certificate_type' sent in the client and
      hello indicates the server, even though certificate types the structure client is only specified
   once in this document.

   The structure able to
      provide to the server, when requested using a certificate_request
      message.  The 'server_certificate_type' in the client hello
      indicates the type of certificates the CertTypeExtension client is defined able to process
      when provided by the server in a subsequent certificate payload.

      The 'client_certificate_type' returned in the server hello
      indicates the certificate type found in the attached certificate
      payload.  Only a single value is permitted.  The
      'server_certificate_type' in the server hello indicates the type
      of certificates the client is requested to provide in a subsequent
      certificate payload.  The value conveyed in the
      'server_certificate_type' MUST be selected from one of the values
      provided in the 'server_certificate_type' sent in the client
      hello.  If the server does not send a certificate_request payload
      or none of the certificates supported by the client (as indicated
      in the 'server_certificate_type' in the client hello) match the
      server-supported certificate types the 'server_certificate_type'
      payload sent in the server hello is omitted.

   The "extension_data" field of this extension contains the
   ClientCertTypeExtension or the ServerCertTypeExtension structure, as follows:
   shown in Figure 5.  The CertificateType structure is an enum with
   with values from TLS Certificate Type Registry.

   struct { client, server
               case client:
                 CertificateType client_certificate_types<1..2^8-1>;
               case server:
                 CertificateType client_certificate_type;
           } ClientOrServerExtension;

   enum { X.509-Accept (0),
          X.509-Offer (1),
          RawPublicKey-Accept (2),
          RawPublicKey-Offer (3),
   } CertificateType; ClientCertTypeExtension;

   struct {
               case client:
                 CertificateType certificate_types<1..2^8-1>; server_certificate_types<1..2^8-1>;
               case server:
                 CertificateType certificate_type; server_certificate_type;
   } CertTypeExtension; ServerCertTypeExtension;

                  Figure 4: 5: CertTypeExtension Structure.

   The '-Offer' postfix indicates that a TLS entity is able to send the
   indicated certificate type to the other communication partner.  The
   '-Accept' postfix indicates that a TLS entity is able to receive the
   indicated certificate type.

   No new cipher suites are required to use raw public keys.  All
   existing cipher suites that support a key exchange method compatible
   with the defined extension can be used.

4.  TLS Handshake Extension

4.1.  Client Hello

   In order to indicate the support of out-of-band raw public keys,
   clients MUST include an extension of type "certificate_type" to the
   extended client hello message.  The "certificate_type" TLS extension
   is assigned the value of [TBD] from the TLS ExtensionType registry.
   This value is used as the extension number for the 'client_certificate_type' and
   'server_certificate_type' extensions in both
   the extended client hello message and the server hello message.
   The hello extension mechanism is described in TLS 1.2 [RFC5246].

4.2.  Server Hello

   If the server receives a client hello that contains the
   "certificate_type" extension
   'client_certificate_type' and 'server_certificate_type' extensions
   and chooses a cipher suite then two three outcomes are possible. possible:

   1.  The server MUST either select a does not support the extension defined in this
       document.  In this case the server returns the server hello
       without the extensions defined in this document.

   2.  The server supports the extension defined in this document and
       has at least one certificate type from in common with the CertificateType field client.  In
       this case it returns the 'server_certificate_type' and indicates
       the selected certificate type value.

   3.  The server supports the extension defined in this document but
       does not have a certificate type in common with the extended client hello or client.  In
       this case the server terminate the session with a fatal alert of
       type "unsupported_certificate".

   The certificate type selected by

   If the TLS server is encoded in also requests a
   CertTypeExtension structure, which is included in certificate from the extended server
   hello message using an client (via
   the certificate_request) it MUST include the
   'client_certificate_type' extension with a value chosen from the list
   of type "certificate_type".  Servers
   that only support X.509 client-supported certificates MAY omit including the
   "certificate_type" extension types (as provided in the extended server hello.
   'client_certificate_type' of the client hello).

   If the client supports indicated the receiption support of raw public keys in the
   'client_certificate_type' extension in the client hello and the
   server is able to provide such a raw public key then the TLS server
   MUST place the SubjectPublicKeyInfo structure into the Certificate
   payload.  The public key algorithm MUST match the selected key
   exchange algorithm.

4.3.  Certificate Request

   The semantics of this message remain the same as in the TLS

4.4.  Other Handshake Messages

   All the other handshake messages are identical to the TLS

4.5.  Client authentication

   Client authentication by the TLS server is supported only through
   authentication of the received client SubjectPublicKeyInfo via an
   out-of-band method method.

5.  Examples

   Figure 5, Figure 6, Figure 7, and Figure 7 8 illustrate example exchanges.

   The first example shows an exchange where the TLS client indicates
   its ability to receive and validate raw public keys.  This keys from the server.
   In our example the client is quite restricted since it is unable to
   process other certificate types sent by the server.  It also does not
   have credentials (at the TLS layer) it could send.  The
   'client_certificate_type' extension indicates this in [1].  When the
   TLS server receives the client hello it processes the certificate_type
   'client_certificate_type' extension.  Since it also has a raw public
   key it indicates in [2] that it had choosen to place the
   SubjectPublicKeyInfo structure into the Certificate payload [3].  The
   client uses this raw public key in the TLS handshake and an out-of-band out-of-
   band technique, such as DANE, to verify its validity.

server_certificate_type=(RawPublicKey) -> // [1]

                         <-  server_hello,
                             server_certificate_type=(RawPublicKey), // [2]
                             certificate, // [3]

finished                  ->

                         <- change_cipher_spec,

Application Data        <------->     Application Data

     Figure 5: 6: Example with Raw Public Key provided by the TLS Server

   In our second example the TLS client as well as the TLS server use
   raw public keys.  This is a use case envisioned for smart object
   networking.  The TLS client in this case is an embedded device that
   is configured with a raw public key for use with TLS and is also able
   to process raw public keys sent by the server.  Therefore, it
   indicates these capabilities in the 'certificate_type' extension in [1].  As in the previously shown
   example the server fulfills the client's request, indicates this via
   the 'RawPublicKey-Offer'in "RawPublicKey" value in the
   certificate_type server_certificate_type payload, and
   provides a raw public key into the Certificate payload back to the
   client (see [3]).  The TLS server, however, demands client
   authentication and therefore a certificate_request is added [4].  The
   certificate_type payload in [2] indicates that the TLS server accepts
   raw public keys.  The TLS client, who has a raw public key pre-provisioned, pre-
   provisioned, returns it in the Certificate payload [5] to the server.

   certificate_type=(RawPublicKey-Offer, RawPublicKey-Accept) ->
client_certificate_type=(RawPublicKey) // [1]
server_certificate_type=(RawPublicKey) // [1]
                         <-  server_hello,
                                            RawPublicKey-Accept) // [2]
                             certificate, // [3]
                             certificate_request, // [4]

certificate, // [5]
finished                  ->

                         <- change_cipher_spec,

Application Data        <------->     Application Data

   Figure 6: 7: Example with Raw Public Key provided by the TLS Server and
                                the Client

   In our last example we illustrate a combination of raw public key and
   X.509 usage.  The client uses a raw public key for client
   authentication but the server provides an X.509 certificate.  This
   exchange starts with the client indicating its ability to process
   X.509 certificates provided by the server, and the ability to send
   raw public keys. keys (see [1]).  The server provides the X.509 certificate
   in [3] with the indication present in [2].  For client authentication,
   however, authentication
   the server indicates in [2] [4] that it is able to support selected the raw public keys key
   format and requests a certificate from the client in [4]. [5].  The TLS
   client provides a raw public key in [5] [6] after receiving and
   processing the TLS server hello message.

   certificate_type=(X.509-Accept, RawPublicKey-Offer) ->
client_certificate_type=(RawPublicKey) // [1]
                         <-  server_hello,
                                     RawPublicKey-Accept), // [2]
                             certificate, // [3]
                             certificate_request, // [4] [5]
certificate, // [5] [6]
finished                  ->

                          <- change_cipher_spec,

Application Data        <------->     Application Data

                   Figure 7: 8: Hybrid Certificate Example

6.  Security Considerations

   The transmission of raw public keys, as described in this document,
   provides benefits by lowering the over-the-air transmission overhead
   since raw public keys are quite naturally smaller than an entire
   certificate.  There are also advantages from a codesize point of view
   for parsing and processing these keys.  The crytographic procedures
   for assocating the public key with the possession of a private key
   also follows standard procedures.

   The main security challenge is, however, how to associate the public
   key with a specific entity.  This information will be needed to make
   authorization decisions.  Without a secure binding, man-in-the-middle
   attacks may be the consequence.  This document assumes that such
   binding can be made out-of-band and we list a few examples in
   Section 1.  DANE [RFC6698] offers one such approach.  If public keys
   are obtained using DANE, these public keys are authenticated via
   DNSSEC.  Pre-configured keys is another out of band method for
   authenticating raw public keys.  While pre-configured keys are not
   suitable for a generic Web-based e-commerce environment such keys are
   a reasonable approach for many smart object deployments where there
   is a close relationship between the software running on the device
   and the server-side communication endpoint.  Regardless of the chosen
   mechanism for out-of-band public key validation an assessment of the
   most suitable approach has to be made prior to the start of a
   deployment to ensure the security of the system.

7.  IANA Considerations

   This document defines

   IANA is asked to register a new TLS extension, "certificate_type",
   assigned a value in the "TLS Certificate Types"
   registry of [TBD] Transport Layer Security (TLS) Extensions
   [TLS-Certificate-Types-Registry], as follows:

   Value: 2
   Description: Raw Public Key
   Reference: [[THIS RFC]]

   This document asks IANA to allocate two new TLS extensions,
   "client_certificate_type" and "server_certificate_type", from the TLS
   ExtensionType registry defined in [RFC5246].  This value is used as the extension number for the  These extensions are
   used in both the client hello message and the server hello message.
   The new extension type is used for certificate type negotiation.  The "certificate_type" extension contains an 8-bit CertificateType
   field, for which a new registry, named "TLS Certificate Types", is
   established in this document, to be maintained by IANA.  The registry
   is segmented in the following way:

   1.  The
   values 0 - 3 are defined carried in Figure 4.

   2.  Values from 3 through 223 decimal inclusive these extensions are assigned via IETF
       Consensus [RFC5226].

   3.  Values taken from 224 decimal through 255 decimal inclusive are
       reserved for Private Use [RFC5226]. the TLS Certificate
   Types registry [TLS-Certificate-Types-Registry].

8.  Acknowledgements

   The feedback from the TLS working group meeting at IETF#81 has
   substantially shaped the document and we would like to thank the
   meeting participants for their input.  The support for hashes of
   public keys has been moved to [I-D.ietf-tls-cached-info] after the
   discussions at the IETF#82 meeting and the feedback from Eric
   Rescorla. meeting.

   We would like to thank the following persons for their review
   comments: Martin Rex, Bill Frantz, Zach Shelby, Carsten Bormann,
   Cullen Jennings, Rene Struik, Alper Yegin, Jim Schaad, Barry Leiba,
   Paul Hoffman, Robert Cragie, Nikos Mavrogiannopoulos, Phil Hunt, John
   Bradley, Klaus Hartke, Stefan Jucker, Kovatsch Matthias, Daniel Kahn
   Gillmor, and James Manger.  Nikos Mavrogiannopoulos contributed the
   design for re-using the certificate type registry.  Barry Leiba
   contributed guidance for the IANA consideration text.  Stefan Jucker,
   Kovatsch Matthias, and Klaus Hartke provided implementation feedback
   regarding the SubjectPublicKeyInfo structure.

   Finally, we would like to thank our TLS working group chairs, Eric
   Rescorla and Joe Salowey, for their guidance and support.

9.  References

9.1.  Normative References

   [PKIX]     Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, May 2008.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

              "TLS Certificate Types Registry", February 2013, <http://

9.2.  Informative References

              Gutmann, P., "ASN.1 Object Dump Program", February 2013,

              Marlinspike, M., "New Tricks for Defeating SSL in
              Practice", February 2009, <

              Shelby, Z., Hartke, K., Bormann, C., and B. Frank,
              "Constrained Application Protocol (CoAP)",
              draft-ietf-core-coap-13 (work in progress), October December 2012.

              Santesson, S. and H. Tschofenig, "Transport Layer Security
              (TLS) Cached Information Extension",
              draft-ietf-tls-cached-info-13 (work in progress),
              September 2012.

   [LDAP]     Sermersheim, J., "Lightweight Directory Access Protocol
              (LDAP): The Protocol", RFC 4511, June 2006.

   [RFC3279]  Bassham, L., Polk, W., and R. Housley, "Algorithms and
              Identifiers for the Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 3279, April 2002.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

   [RFC6698]  Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
              of Named Entities (DANE) Transport Layer Security (TLS)
              Protocol: TLSA", RFC 6698, August 2012.

Appendix A.  Example Encoding

   For example, the following hex sequence describes a
   SubjectPublicKeyInfo structure inside the certificate payload:

          0     1     2     3     4     5     6     7     8     9
   1  | 0x30, 0x81, 0x9f, 0x30, 0x0d, 0x06, 0x09, 0x2a, 0x86, 0x48,
   2  | 0x86, 0xf7, 0x0d, 0x01, 0x01, 0x01, 0x05, 0x00, 0x03, 0x81,
   3  | 0x8d, 0x00, 0x30, 0x81, 0x89, 0x02, 0x81, 0x81, 0x00, 0xcd,
   4  | 0xfd, 0x89, 0x48, 0xbe, 0x36, 0xb9, 0x95, 0x76, 0xd4, 0x13,
   5  | 0x30, 0x0e, 0xbf, 0xb2, 0xed, 0x67, 0x0a, 0xc0, 0x16, 0x3f,
   6  | 0x51, 0x09, 0x9d, 0x29, 0x2f, 0xb2, 0x6d, 0x3f, 0x3e, 0x6c,
   7  | 0x2f, 0x90, 0x80, 0xa1, 0x71, 0xdf, 0xbe, 0x38, 0xc5, 0xcb,
   8  | 0xa9, 0x9a, 0x40, 0x14, 0x90, 0x0a, 0xf9, 0xb7, 0x07, 0x0b,
   9  | 0xe1, 0xda, 0xe7, 0x09, 0xbf, 0x0d, 0x57, 0x41, 0x86, 0x60,
   10 | 0xa1, 0xc1, 0x27, 0x91, 0x5b, 0x0a, 0x98, 0x46, 0x1b, 0xf6,
   11 | 0xa2, 0x84, 0xf8, 0x65, 0xc7, 0xce, 0x2d, 0x96, 0x17, 0xaa,
   12 | 0x91, 0xf8, 0x61, 0x04, 0x50, 0x70, 0xeb, 0xb4, 0x43, 0xb7,
   13 | 0xdc, 0x9a, 0xcc, 0x31, 0x01, 0x14, 0xd4, 0xcd, 0xcc, 0xc2,
   14 | 0x37, 0x6d, 0x69, 0x82, 0xd6, 0xc6, 0xc4, 0xbe, 0xf2, 0x34,
   15 | 0xa5, 0xc9, 0xa6, 0x19, 0x53, 0x32, 0x7a, 0x86, 0x0e, 0x91,
   16 | 0x82, 0x0f, 0xa1, 0x42, 0x54, 0xaa, 0x01, 0x02, 0x03, 0x01,
   17 | 0x00, 0x01

      Figure 9: Example SubjectPublicKeyInfo Structure Byte Sequence.

   The decoded byte-sequence shown in Figure 9 (for example using
   Peter's ASN.1 decoder [ASN.1-Dump]) illustrates the structure, as
   shown in Figure 10.

   Offset  Length   Description
      0     3+159:   SEQUENCE {
      3      2+13:     SEQUENCE {
      5       2+9:      OBJECT IDENTIFIER Value (1 2 840 113549 1 1 1)
                 :             PKCS #1, rsaEncryption
     16       2+0:      NULL
                 :      }
     18     3+141:    BIT STRING, encapsulates {
     22     3+137:      SEQUENCE {
     25     3+129:        INTEGER Value (1024 bit)
    157       2+3:        INTEGER Value (65537)
                 :        }
                 :      }
                 :    }

      Figure 10: Decoding of Example SubjectPublicKeyInfo Structure.

Authors' Addresses

   Paul Wouters (editor)
   Red Hat


   Hannes Tschofenig (editor)
   Nokia Siemens Networks
   Linnoitustie 6
   Espoo  02600

   Phone: +358 (50) 4871445
   John Gilmore
   PO Box 170608
   San Francisco, California  94117

   Phone: +1 415 221 6524

   Samuel Weiler
   SPARTA, Inc.
   7110 Samuel Morse Drive
   Columbia, Maryland  21046


   Tero Kivinen
   Eerikinkatu 28
   HELSINKI  FI-00180