This is a purely informative rendering of an RFC that includes verified errata. This rendering may not be used as a reference.

The following 'Verified' errata have been incorporated in this document: EID 1047, EID 2355, EID 2358, EID 2359, EID 2362
Network Working Group                                            J. Park
Request for Comments: 4683                                        J. Lee
Category: Standards Track                                         H. Lee
                                                                    KISA
                                                                 S. Park
                                                                   BCQRE
                                                                 T. Polk
                                                                    NIST
                                                            October 2006


                Internet X.509 Public Key Infrastructure
                  Subject Identification Method (SIM)


Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This document defines the Subject Identification Method (SIM) for
   including a privacy-sensitive identifier in the subjectAltName
   extension of a certificate.

   The SIM is an optional feature that may be used by relying parties to
   determine whether the subject of a particular certificate is also the
   person corresponding to a particular sensitive identifier.

Table of Contents

   1. Introduction ....................................................2
      1.1. Key Words ..................................................5
   2. Symbols .........................................................6
   3. Requirements ....................................................6
      3.1. Security Requirements ......................................6
      3.2. Usability Requirements .....................................7
      3.3. Solution ...................................................7
   4. Procedures ......................................................8
      4.1. SII and SIItype ............................................8
      4.2. User Chosen Password .......................................9
      4.3. Random Number Generation ...................................9
      4.4. Generation of SIM ..........................................9
      4.5. Encryption of PEPSI .......................................10
      4.6. Certification Request .....................................10
      4.7. Certification .............................................11
   5. Definition .....................................................11
      5.1. SIM Syntax ................................................11
      5.2. PEPSI .....................................................12
      5.3. Encrypted PEPSI ...........................................12
   6. Example Usage of SIM ...........................................13
   7. Name Constraints ...............................................13
   8. Security Considerations ........................................14
   9. Acknowledgements ...............................................15
   10. IANA Considerations ...........................................15
   11. References ....................................................15
      11.1. Normative References .....................................15
      11.2. Informative References ...................................15
   Appendix A.  "Compilable" ASN.1 Module, 1988 Syntax ...............18

1.  Introduction

   A Certification Authority (CA) issues X.509 public key certificates
   to bind a public key to a subject.  The subject is specified through
   one or more subject names in the "subject" or "subjectAltName" fields
   of a certificate.  The "subject" field contains a hierarchically
   structured distinguished name.  The "subjectAltName field" may
   contain an electronic mail address, IP address, or other name forms
   that correspond to the subject.

   For each particular CA, a subject name corresponds to a unique
   person, device, group, or role.  The CA will not knowingly issue
   certificates to multiple entities under the same subject name.  That
   is, for a particular certificate issuer, all currently valid
   certificates asserting the same subject name(s) are bound to the same
   entity.

   Where the subject is a person, the name that is specified in the
   subject field of the certificate may reflect the name of the
   individual and affiliated entities (e.g., their corporate
   affiliation).  In reality, however, there are individuals or
   corporations that have the same or similar names.  It may be
   difficult for a relying party (e.g., a person or application) to
   associate the certificate with a specific person or organization
   based solely on the subject name.  This ambiguity presents a problem
   for many applications.

   In some cases, applications or relying parties need to ensure that
   the subject of certificates issued by different CAs are in fact the
   same entity.  This requirement may be met by including a "permanent
   identifier" in all certificates issued to the same subject, which is
   unique across multiple CAs.  By comparing the "permanent identifier",
   the relying party may identify certificates from different CAs that
   are bound to the same subject.  This solution is defined in [RFC
   4043].

   In many cases, a person's or corporation's identifier (e.g., a Social
   Security Number) is regarded as sensitive, private, or personal data.
   Such an identifier cannot simply be included as part of the subject
   field, since its disclosure may lead to misuse.  Therefore, privacy-
   sensitive identifiers of this sort should not be included in
   certificates in plaintext form.

   On the other hand, such an identifier is not actually a secret.
   People choose to disclose these identifiers for certain classes of
   transactions.  For example, a person may disclose a Social Security
   Number to open a bank account or obtain a loan.  This is typically
   corroborated by presenting physical credentials (e.g., a driver's
   license) that confirm the person's name or address.

   To support such applications in an online environment, relying
   parties need to determine whether the subject of a particular
   certificate is also the person corresponding to a particular
   sensitive identifier.  Ideally, applications would leverage the
   applicants' electronic credential (e.g., the X.509 public key
   certificate) to corroborate this identifier, but the subject field of
   a certificate often does not provide sufficient information.

   To fulfill these demands, this specification defines the Subject
   Identification Method (SIM) and the Privacy-Enhanced Protected
   Subject Information (PEPSI) format for including a privacy sensitive
   identifier in a certificate.  Although other solutions for binding
   privacy-sensitive identifiers to a certificate could be developed,
   the method specified in this document has especially attractive
   properties.  This specification extends common PKI practices and

   mechanisms to allow privacy-sensitive identifiers to be included in
   the certificate as well.  The SIM mechanism also permits the subject
   to control exposure of the sensitive identifier; when the subject
   chooses to expose the sensitive identifier, relying parties can
   verify the binding.  Specifically:

   (1) A Public Key Infrastructure (PKI) depends upon a trusted third
   party -- the CA -- to bind one or more identities to a public key.
   Traditional PKI implementations bind X.501 distinguished names to the
   public key, but identity may also be specified in terms of RFC 822
   addresses or DNS names.  The SIM specification allows the same
   trusted third party -- the CA -- that binds a name to the public key
   to include a privacy-sensitive identifier in the certificate as well.
   Since the relying party (RP) already trusts the CA to issue
   certificates, it is a simple extension to cover verification and
   binding of a sensitive identifier as well.  This binding could be
   established separately, by another trusted third party, but this
   would complicate the infrastructure.

   (2) This specification leverages standard PKI extensions to achieve
   new functional goals with a minimum of new code.  This specification
   encodes the sensitive identifier in the otherName field in the
   alternative subject name extension.  Since otherName field is widely
   used, this solution leverages a certificate field that is often
   populated and processed.  (For example, smart card logon
   implementations generally rely upon names encoded in this field.)
   Whereas implementations of this specification will require some SIM-
   specific code, an alternative format would increase cost without
   enhancing security.  In addition, that has no impact on
   implementations that do not process sensitive identifiers.

   (3) By explicitly binding the public key to the identifier, this
   specification allows the relying party to confirm the claimant's
   identifier and confirm that the claimant is the subject of that
   identifier.  That is, proof of possession of the private key confirms
   that the claimant is the same person whose identity was confirmed by
   the PKI (CA or RA, depending upon the architecture).

   To achieve the same goal in a separate message (e.g., a signed and
   encrypted Secure MIME (S/MIME) object), the message would need to be
   bound to the certificate or an identity in the certificate (e.g., the
   X.501 distinguished name).  The former solution is problematic, since
   certificates expire.  The latter solution may cause problems if names
   are ever reused in the infrastructure.  An explicit binding in the
   certificate is a simpler solution, and more reliable.

   (4) This specification allows the subject of the privacy-sensitive
   identifier to control the distribution and level of security applied
   to the identifier.  The identifier is only disclosed when the subject
   chooses to disclose it, even if the certificate is posted in a public
   directory.  By choosing a strong password, the subject can ensure
   that the identifier is protected against brute force attacks.  This
   specification permits subjects to selectively disclose an identifier
   where they deem it appropriate, which is consistent with common use
   of such identifiers.

   (5) Certificates that contain a sensitive identifier may still be
   used to support other applications.  A party that obtains a
   certificate containing a sensitive identifier, but to whom the
   subject does not choose to disclose the identifier, must perform a
   brute force attack to obtain the identifier.  By selecting a strong
   hash algorithm, this attack becomes computationally infeasible.
   Moreover, when certificates include privacy-sensitive identifiers as
   described in this specification, each certificate must be attacked
   separately.  Finally, the subjects can use this mechanism to prove
   they possess a certificate containing a particular type of identifier
   without actually disclosing it to the relying party.

   This feature MUST be used only in conjunction with protocols that
   make use of digital signatures generated using the subject's private
   key.

   In addition, this document defines an Encrypted PEPSI (EPEPSI) so
   that sensitive identifier information can be exchanged during
   certificate issuance processes without disclosing the identifier to
   an eavesdropper.

   This document is organized as follows:

   - Section 3 establishes security and usability requirements;
   - Section 4 provides an overview of the mechanism;
   - Section 5 defines syntax and generation rules; and
   - Section 6 provides example use cases.

1.1.  Key Words

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

2.  Symbols

   The following cryptography symbols are defined in this document.

       H()        Cryptographically secure hash algorithm.
                  SHA-1 [FIPS 180-1] or a more secure hash function is
                  required.

       SII        Sensitive Identification Information
                  (e.g., Social Security Number).

       SIItype    Object Identifier that identifies the type of SII.

       P          A user-chosen password.

       R          The random number value generated by a Registration
                  Authority (RA).

       PEPSI      Privacy-Enhanced Protected Subject Information.
                  Calculated from the input value P, R, SIItype, SII
                  using two iteration of H().

       E()        The encryption algorithm to encrypt the PEPSI value.

       EPEPSI     Encrypted PEPSI.

       D()        The decryption algorithm to decrypt the EPEPSI.

3.  Requirements

3.1.  Security Requirements

   We make the following assumptions about the context in which SIM and
   PEPSI are to be employed:

     - Alice, a certificate holder, with a sensitive identifier SIIa
       (such as her Social Security Number)
     - Bob, a relying party who will require knowledge of Alice's SIIa
     - Eve, an attacker who acquires Alice's certificate
     - An RA to whom Alice must divulge her SIIa
     - A CA who will issue Alice's certificate

   We wish to design SIM and PEPSI, using a password that Alice chooses,
   that has the following properties:

     - Alice can prove her SII, SIIa to Bob.

     - Eve has a large work factor to determine Alice's SIIa from
       Alice's certificate, even if Alice chooses a weak password, and a
       very large work factor if Alice chooses a good password.
     - Even if Eve can determine SIIa, she has an equally hard problem
       to find any other SII values from any other PEPSI; that is, there
       is nothing she can pre-compute that helps her attack PEPSIs in
       other certificates, and nothing she learns from a successful
       attack that helps in any other attack.
     - The CA does not learn Alice's SIIa except in the case where the
       CA needs to validate the SII passed by the RA.
     - The CA can treat the SIM as an additional name form in the
       "subjectAltName" extension with no special processing.
     - Alice cannot find another SII (SIIx), and a password (P), that
       will allow her to use her certificate to assert a false SII.

3.2.  Usability Requirements

   In addition to the security properties stated above, we have the
   following usability requirements:

     - When SIM and PEPSI are used, any custom processing occurs at the
       relying party.  Alice can use commercial off-the-shelf software
       (e.g., a standard browser) without modification in conjunction
       with a certificate containing a SIM value.

3.3.  Solution

   We define SIM as: R || PEPSI
             where PEPSI = H(H( P || R || SIItype || SII))

   The following steps describe construction and use of SIM:

   1.      Alice picks a password P, and gives P, SIItype, and SII to
           the RA (via a secure channel).
   2.      The RA validates SIItype and SII; i.e., it determines that
           the SII value is correctly associated with the subject and
           the SIItype is correct.
   3.      The RA generates a random value R.
   4.      The RA generates the SIM = (R || PEPSI) where PEPSI = H(H(P
           || R || SIItype || SII)).
   5.      The RA sends the SIM to Alice by some out-of-band means and
           also passes it to the CA.
   6.      Alice sends a certRequest to CA.  The CA generates Alice's
           certificate including the SIM as a form of otherName from the
           GeneralName structure in the subjectAltName extension.
   7.      Alice sends Bob her Cert, as well as P, SIItype, and SII.
           The latter values must be communicated via a secure
           communication channel, to preserve their confidentiality.

   8.      Bob can compute PEPSI' = H(H(P || R || SIItype || SII)) and
           compare SIM' = R || PEPSI' to the SIM value in Alice's
           certificate, thereby verifying SII.

   If Alice's SII value is not required by Bob (Bob already knows
   Alice's SII and does not require it), then steps 7 and 8 are as
   follows:

   7.      Alice sends Bob her Cert and P.  P must be sent via a secure
           communication channel, to preserve its confidentiality.
   8.      Bob can compute PEPSI' = H(H(P || R || SIItype || SII)) and
           compare SIM' = R || PEPSI' to the value in the SIM, thereby
           verifying SII.

   If Alice wishes to prove she is the subject of an RA-validated
   identifier, without disclosing her identifier to Bob, then steps 7
   and 8 are as follows:

   7.      Alice sends the intermediate value H(P || R || SIItype ||
           SII) and her certificate to Bob.
   8.      Bob can get R from the SIM in the certificate, then compute H
           (intermediate value) and compare it to the value in SIM,
           thereby verifying Alice's knowledge of P and SII.

   Eve has to exhaustively search the H(P || R || SIItype || SII) space
   to find Alice's SII.  This is a fairly hard problem even if Alice
   uses a poor password, because of the size of R (as specified later),
   and a really hard problem if Alice uses a fairly good password (see
   Section 8).

   Even if Eve finds Alice's P and SII, or constructs a massive
   dictionary of P and SII values, it does not help find any other SII
   values, because a new R is used for each PEPSI and SIM.

4.  Procedures

4.1.  SII and SIItype

   The user presents evidence that a particular SII has been assigned to
   him/her.  The SIItype is an Object Identifier (OID) that defines the
   format and scope of the SII value.  For example, in Korea, one
   SIItype is defined as follows:

   -- KISA specific arc
   id-KISA OBJECT IDENTIFIER ::=
     {iso(1) member-body(2) korea(410) kisa(200004)}

   -- KISA specific OIDs
   id-npki OBJECT IDENTIFIER ::= {id-KISA 10}
   id-attribute OBJECT IDENTIFIER ::= {id-npki 1}
   id-kisa-identifyData OBJECT IDENTIFIER ::= {id-attribute 1}
   id-VID OBJECT IDENTIFIER ::= {id-kisa-identifyData 10}
   id-SII OBJECT IDENTIFIER ::= {id-VID 1}

   For closed communities, the SIItype value may be assigned by the CA
   itself, but it is still recommended that the OID be registered.

4.2.  User Chosen Password

   The user selects a password as one of the input values for computing
   the SIM.  The strength of the password is critical to protection of
   the user's SII, in the following sense.  If an attacker has a
   candidate SII value, and wants to determine whether the SIM value in
   a specific subject certificate, P is the only protection for the SIM.
   The user should be encouraged to select passwords that will be
   difficult to be guessed, and long enough to protect against brute
   force attacks.

   Implementations of this specification MUST permit a user to select
   passwords of up to 28 characters.  RAs SHOULD implement password
   filter rules to prevent user selection of trivial passwords.  See
   [FIPS 112] and [FIPS 180-1] for security criteria for passwords and
   an automated password generator algorithm that randomly creates
   simple pronounceable syllables as passwords.

4.3.  Random Number Generation

   The RA generates a random number, R.  A new R MUST be generated for
   each SIM.  The length of R MUST be the same as the length of the
   output of the hash algorithm H.  For example, if H is SHA-1, the
   random number MUST be 160 bits.

   A Random Number Generator (RNG) that meets the requirements defined
   in [FIPS 140-2] and its use is strongly recommended.

4.4.  Generation of SIM

EID 2355 (Verified) is as follows:

Section: 4.4

Original Text:

On page 10, the second-to-last paragraph of Section 4.4 says:

   Note that a secure communication channel MUST be used to pass P and
|  SII passing from the end entity to the RA, to protect them from
   disclosure or modification.

It should say:

   Note that a secure communication channel MUST be used to pass P and
|  SII from the end entity to the RA, to protect them from disclosure or
   modification.

Corrected Text:

See above.
Notes:
None
The SIM in the subjectAltName extension within a certificate identifies an entity, even if multiple subjectAltNames appear in a certificate. RAs MUST calculate the SIM value with the designated inputs according to the following algorithm: SIM = R || PEPSI where PEPSI = H(H(P || R || SIItype || SII)) The SII is made known to an RA at user enrollment. Both SHA-1 and SHA-256 MUST be supported for generation and verification of PEPSI values. This specification does not preclude use of other one-way hash functions, but SHA-1 or SHA-256 SHOULD be used wherever interoperability is a concern. Note that a secure communication channel MUST be used to pass P and SII passing from the end entity to the RA, to protect them from disclosure or modification. The syntax and the associated OID for SIM are also provided in the ASN.1 modules in Section 5.1. Also, Section 5.2 describes the syntax for PEPSI in the ASN.1 modules. 4.5. Encryption of PEPSI It may be required that the CA (not just the RA) verifies SII before issuing a certificate. To meet this requirement, RA SHOULD encrypt the SIItype, SII, and SIM and send the result to the CA by a secure channel. The user SHOULD also encrypt the same values and send the result to the CA in his or her certificate request message. Then the CA compares these two results for verifying the user's SII. Where the results from RA and the user are the EPEPSI. EPEPSI = E(SIItype || SII || SIM) When the EPEPSI is used in a user certificate request, it is in regInfo of [RFC4211] and [RFC2986]. Note: Specific encryption/decryption methods are not defined in this document. For transmission of the PEPSI value from a user to a CA, the certificate request protocol employed defines how encryption is performed. For transmission of this data between an RA and a CA, the details of how encryption is performed is a local matter. The syntax and the associated OID for EPEPSI is provided in the ASN.1 modules in Section 5.3. 4.6. Certification Request As described above, a certificate request message MAY contain the SIM. [RFC2986] and [RFC4211] are widely used message syntaxes for certificate requests. Basically, a PKCS#10 message consists of a distinguished name, a public key, and an optional set of attributes, collectively signed by the end entity. The SIM alternative name MUST be placed in the subjectAltName extension if this certificate request format is used. If a CA verifies SII before issuing the certificate, the value of SIM in the certification request MUST be conveyed in the EPEPSI form and provided by the subject. 4.7. Certification A CA that issues certificates containing the SIM includes the SIM as a form of otherName from the GeneralName structure in the "subjectAltName" extension. In an environment where a CA verifies SII before issuing the certificate, a CA decrypts the EPEPSI values it receives from both the user and the RA, and compares them. It then validates that the SII value is correctly bound to the subject. SIItype, SII, SIM = D(EPEPSI) 5. Definition 5.1. SIM Syntax
EID 2358 (Verified) is as follows:

Section: 5.1

Original Text:

The ASN.1 at the bottom of page 11 says:

        SIM ::= SEQUENCE {
            hashAlg          AlgorithmIdentifier,
            authorityRandom  OCTET STRING,   -- RA-chosen random number
                                             -- used in computation of
                                             -- pEPSI
|           pEPSI            OCTET STRING    -- hash of HashContent
                                             -- with algorithm hashAlg
        }

It should say:

        SIM ::= SEQUENCE {
            hashAlg          AlgorithmIdentifier,
            authorityRandom  OCTET STRING,   -- RA-chosen random number
                                             -- used in computation of
                                             -- pEPSI
|           pEPSI            OCTET STRING    -- hash of hash of
|                                            -- HashContent with
                                             -- algorithm hashAlg
        }

Corrected Text:

See above.
Notes:
Rationale:
PEPSI is an iterated hash; see Section 4.4 where the last
line on page 9 says,
where PEPSI = H(H(P || R || SIItype || SII))
-----------------v-------
and Section 5.2 for the definition of HashContent.
This section specifies the syntax for the SIM name form included in the subjectAltName extension. The SIM is composed of the three fields: the hash algorithm identifier, the authority-chosen random value, and the value of the PEPSI itself. id-pkix OBJECT IDENTIFIER ::= { iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) } id-on OBJECT IDENTIFIER ::= { id-pkix 8 } id-on-SIM OBJECT IDENTIFIER ::= { id-on 6 } SIM ::= SEQUENCE { hashAlg AlgorithmIdentifier, authorityRandom OCTET STRING, -- RA-chosen random number -- used in computation of -- pEPSI pEPSI OCTET STRING -- hash of HashContent -- with algorithm hashAlg } 5.2. PEPSI This section specifies the syntax for the PEPSI. The PEPSI is generated by performing the same hash function twice. The PEPSI is generated over the ASN.1 structure HashContent. HashContent has four values: the user-selected password, the authority-chosen random number, the identifier type, and the identifier itself. HashContent ::= SEQUENCE { userPassword UTF8String, -- user-supplied password authorityRandom OCTET STRING, -- RA-chosen random number identifierType OBJECT IDENTIFIER, -- SIItype identifier UTF8String -- SII } Before calculating a PEPSI, conforming implementations MUST process the userPassword with the six-step [LDAPBIS STRPREP] string preparation algorithm, with the following changes: * In step 2, Map, the mapping shall include processing of characters commonly mapped to nothing, as specified in Appendix B.1 of [RFC3454]. * Omit step 6, Insignificant Character Removal. 5.3. Encrypted PEPSI
EID 2359 (Verified) is as follows:

Section: 5.3

Original Text:

At the bottom of page 12, Section 5.3 says:

   id-regEPEPSI OBJECT IDENTIFIER ::= { id-pkip 3 }

For instance, a note should be added at the bottom of page 12:

   id-regEPEPSI OBJECT IDENTIFIER ::= { id-pkip 3 }
|
|  where id-pkip is defined in [RFC4211].

Corrected Text:

See above.
Notes:
The OID, 'id-pkip' is neither defined within RFC 4683 nor imported.
Eventually, I found it being defined in RFC 4211.
That should be made explicit in Section 5.3 of RFC 4683 !
This section describes the syntax for the Encrypted PEPSI. The Encrypted PEPSI has three fields: identifierType, identifier, and SIM. EncryptedPEPSI ::= SEQUENCE { identifierType OBJECT IDENTIFIER, -- SIItype identifier UTF8String, -- SII sIM SIM -- Value of the SIM } When it is used in a certificate request, the OID in 'regInfo' of [RFC4211] and [RFC2986] is as follows: id-regEPEPSI OBJECT IDENTIFIER ::= { id-pkip 3 } 6. Example Usage of SIM Depending on different security environments, there are three possible use cases with SIM. 1. When a relying party does not have any information about the certificate user. 2. When a relying party already knows the SII of the certificate user. 3. When the certificate user does not want to disclose his SII. For the use case 1, the SII and a user-chosen password P (which only the user knows) must be sent to a relying party via a secure communication channel; the certificate including the SIM also must be transmitted. The relying party acquires R from the certificate. The relying party can verify that the SII was validated by the CA (or RA) and is associated with the entity that presented the password and certificate. In this case, the RP learns which SII is bound to the subject as a result of the procedure. In case 2, a certificate user transmits only the password, P, and the certificate. The rest of the detailed procedure is the same as case 1, but here the relying party supplies the SII value, based on its external knowledge of that value. The purpose in this case is to enable the RP to verify that the subject is bound to the SII, presumably because the RP identifies the subject based on this SII. In the last case, the certificate user does not want to disclose his or her SII because of privacy concerns. Here the only information sent by a certificate subject is the intermediate value of the PEPSI, H(R || P || SIItype || SII). This value MUST be transmitted via a secure channel, to preserve its confidentiality. Upon receiving this value, the relying party applies the hash function to the intermediate PEPSI value sent by the user, and matches it against the SIM value in the user's certificate. The relying party does not learn the user's SII value as a result of this processing, but the relying party can verify the fact that the user knows the right SII and password. This gives the relying party more confidence that the user is the certificate subject. Note that this form of user identity verification is NOT to be used in lieu of standard certificate validation procedures, but rather in addition to such procedures. 7. Name Constraints The SIM value is stored as an otherName of a subject alternative name; however, there are no constraints that can be placed on this form of the name. 8. Security Considerations Confidentiality for a SIM value is created by the iterated hashing of the R, P, and SII values. A SIM value depends on two properties of a hash function: the fact that it cannot be inverted and the fact that collisions (especially with formatted data) are rare. The current attacks by [WANG] are not applicable to SIM values since the end entity supplying the SII and SIItype values does not supply all of the data being hashed; i.e., the RA provides the R value. In addition, a fairly good password is needed to protect against guessing attacks on SIMs. Due to the short length of many SIIs, it is possible that an attacker may be able to guess it with partial information about gender, age, and date of birth. SIItype values are very limited. Therefore, it is important for users to select a fairly good password to prevent an attacker from determining whether a guessed SII is accurate. This protocol assumes that Bob is a trustworthy relying party who will not reuse the Alice's information. Otherwise, Bob could "impersonate" Alice if only knowledge of P and SII were used to verify a subject's claimed identity. Thus, this protocol MUST be used only with the protocols that make use of digital signatures generated using the subject's private key. Digital signatures are used by a message sender to demonstrate knowledge of the private key corresponding to the public key in a certificate, and thus to authenticate and bind his or her identity to a signed message. However, managing a private key is vulnerable under certain circumstances. It is not fully guaranteed that the claimed private key is bound to the subject of a certificate. So, the SIM can enhance verification of user identity. Whenever a certificate needs to be updated, a new R SHOULD be generated and the SIM SHOULD be recomputed. Repeating the value of the SIM from a previous certificate permits an attacker to identify certificates associated with the same individual, which may be undesirable for personal privacy purposes. 9. Acknowledgements Jim Schaad (Soaring Hawk Consulting), Seungjoo Kim, Jaeho Yoon, Baehyo Park (KISA), Bill Burr, Morrie Dworkin (NIST), and the Internet Security Technology Forum (ISTF) have significantly contributed to work on the SIM and PEPSI concept and identified a potential security attack. Also their comments on the set of desirable properties for the PEPSI and enhancements to the PEPSI were most illumination. Also, thanks to Russell Housley, Stephen Kent, and Denis Pinkas for their contributions to this document. 10. IANA Considerations In the future, IANA may be asked to establish a registry of object identifiers to promote interoperability in the specification of SII types. 11. References 11.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2986] Nystrom, M. and B. Kaliski, "PKCS #10: Certification Request Syntax Specification Version 1.7", RFC 2986, November 2000. [RFC3454] Hoffman, P. and M. Blanchet, "Preparation of Internationalized Strings ("stringprep")", RFC 3454, December 2002. [RFC4043] Pinkas, D. and T. Gindin, "Internet X.509 Public Key Infrastructure Permanent Identifier", RFC 4043, May 2005. [RFC4211] Schaad, J., "Internet X.509 Public Key Infrastructure Certificate Request Message Format (CRMF)", RFC 4211, September 2005. 11.2. Informative References [LDAPBIS STRPREP] Zeilenga, K., "LDAP: Internationalized String Preparation", Work in Progress. [FIPS 112] Fedreal Information Processing Standards Publication (FIPS PUB) 112, "Password Usage", 30 May 1985. [FIPS 180-1] Federal Information Processing Standards Publication (FIPS PUB) 180-1, "Secure Hash Standard", 17 April 1995. [FIPS 140-2] Federal Information Processing Standards Publication (FIPS PUB) 140-2, "Security Requirements for Cryptographic Modules", 25 May 2001. [WANG] Xiaoyun Wang, Yiqun Lisa Yin, and Hongbo Yu, "Finding Collisions in the Full SHA-1", Crypto'05. <http://www.infosec.sdu.edu.cn/paper/sha1-crypto- auth-new-2-yao.pdf> Authors' Addresses Jongwook Park Korea Information Security Agency 78, Garak-Dong, Songpa-Gu, Seoul, 138-803 REPUBLIC OF KOREA Phone: 2-405-5432 EMail: khopri@kisa.or.kr Jaeil Lee 78, Garak-Dong, Songpa-Gu, Seoul, 138-803 REPUBLIC OF KOREA Korea Information Security Agency Phone: 2-405-5300 EMail: jilee@kisa.or.kr Hongsub Lee Korea Information Security Agency 78, Garak-Dong, Songpa-Gu, Seoul, 138-803 REPUBLIC OF KOREA Phone: 2-405-5100 EMail: hslee@kisa.or.kr Sangjoon Park BCQRE Co.,Ltd Yuil Bldg. Dogok-dong 411-14, Kangnam-ku, Seoul, 135-270 REPUBLIC OF KOREA EMail: sjpark@bcqre.com Tim Polk National Institute of Standards and Technology 100 Bureau Drive, MS 8930 Gaithersburg, MD 20899 EMail: tim.polk@nist.gov Appendix A. "Compilable" ASN.1 Module, 1988 Syntax
EID 1047 (Verified) is as follows:

Section: A

Original Text:



Corrected Text:

id-pkip
 FROM PKIXCRMF-2005
  { iso(1) identified-organization(3) dod(6) internet(1) security(5)
    mechanisms(5) pkix(7) id-mod(0) id-mod-crmf2005(36) }
Notes:
As exposed in Errata 2359 above, the OID 'id-pkip' used on page 19
needs to be IMPORTed from the PKIXCRMF-2005 ASN.1 module in
Appendix B of RFC 4211 -- otherwise the PKIXSIM ASN.1 module
in Appendix A of RFC 4683 will not compile.
EID 2362 (Verified) is as follows:

Section: A

Original Text:

The change exposed in Errata 2358 has to be applied to the
collected ASN.1 as well.

Corrected Text:


Notes:
None
PKIXSIM {iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-sim2005(38) } DEFINITIONS EXPLICIT TAGS ::= BEGIN -- EXPORTS ALL IMPORTS AlgorithmIdentifier, AttributeTypeAndValue FROM PKIX1Explicit88 {iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-pkix1-explicit(18)} -- SIM -- SIM certificate OID id-pkix OBJECT IDENTIFIER ::= { iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) } id-on OBJECT IDENTIFIER ::= { id-pkix 8 } id-on-SIM OBJECT IDENTIFIER ::= { id-on 6 } -- Certificate Syntax SIM ::= SEQUENCE { hashAlg AlgorithmIdentifier, authorityRandom OCTET STRING, -- RA-chosen random number -- used in computation of -- pEPSI pEPSI OCTET STRING -- hash of HashContent -- with algorithm hashAlg } -- PEPSI UTF8String ::= [UNIVERSAL 12] IMPLICIT OCTET STRING -- The content of this type conforms to RFC 2279 HashContent ::= SEQUENCE { userPassword UTF8String, -- user-supplied password authorityRandom OCTET STRING, -- RA-chosen random number identifierType OBJECT IDENTIFIER, -- SIItype identifier UTF8String -- SII } -- Encrypted PEPSI -- OID for encapsulated content type id-regEPEPSI OBJECT IDENTIFIER ::= { id-pkip 3 } EncryptedPEPSI ::= SEQUENCE { identifierType OBJECT IDENTIFIER, -- SIItype identifier UTF8String, -- SII sIM SIM -- Value of the SIM } END Full Copyright Statement Copyright (C) The Internet Society (2006). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Intellectual Property The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgement Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA).