Internet Engineering Task Force (IETF) K. Moriarty, Ed. Request for Comments: 7292 EMC Category: Informational M. Nystrom ISSN: 2070-1721 Microsoft Corporation S. Parkinson A. Rusch M. Scott RSA July 2014
PKCS #12: Personal Information Exchange Syntax v1.1
Abstract
PKCS #12 v1.1 describes a transfer syntax for personal identity information, including private keys, certificates, miscellaneous secrets, and extensions. Machines, applications, browsers, Internet kiosks, and so on, that support this standard will allow a user to import, export, and exercise a single set of personal identity information. This standard supports direct transfer of personal information under several privacy and integrity modes.
This document represents a republication of PKCS #12 v1.1 from RSA Laboratories' Public Key Cryptography Standard (PKCS) series. By publishing this RFC, change control is transferred to the IETF.
IESG Note
The IESG thanks RSA Laboratories for transferring change control to the IETF. Enhancements to this specification that preserve backward compatibility are expected in an upcoming IETF Standards Track document.
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Status of This Memo
This document is not an Internet Standards Track specification; it is published for informational purposes.
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Not all documents approved by the IESG are a candidate for any level of Internet Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc7292.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
This document represents a republication of PKCS #12 v1.1 from RSA Laboratories' Public Key Cryptography Standard (PKCS) series. By publishing this RFC, change control is transferred to the IETF. RSA and its parent company EMC reserve the right to continue publishing and distributing PKCS #12 v1.1 and its predecessors.
The body of this document, except for the Security Considerations section, is taken directly from the PKCS #12 v1.1 specification. The list of references and the in-line cites have been updated or added where appropriate to cite the most current documents in addition to those current at the original publication of PKCS #12 v1.1.
This standard describes a transfer syntax for personal identity information, including private keys, certificates, miscellaneous secrets, and extensions. Machines, applications, browsers, Internet kiosks, and so on, that support this standard will allow a user to import, export, and exercise a single set of personal identity information.
This standard supports direct transfer of personal information under several privacy and integrity modes. The most secure of the privacy and integrity modes require the source and destination platforms to have trusted public/private key pairs usable for digital signatures and encryption, respectively. The standard also supports lower- security, password-based privacy and integrity modes for those cases where trusted public/private key pairs are not available.
This standard should be amenable to both software and hardware implementations. Hardware implementations offer physical security in tamper-resistant tokens such as smart cards and Personal Computer Memory Card International Association (PCMCIA) devices.
This standard can be viewed as building on PKCS #8 [15] [24] by including essential but ancillary identity information along with private keys and by instituting higher security through public-key privacy and integrity modes.
This document transfers PKCS #12 [16] into the IETF and includes some minor changes from the authors for this submission.
o Addition of hash algorithms.
o Incorporation of Technical Corrigendum #1, which makes some minor corrections to the ASN.1 syntax.
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o Removed (from the ASN.1 syntax) 1024 as an example of the iteration count.
o Addition of a recommendation that the technique in Appendix B no longer be used for a specific mode (password privacy mode) and that techniques from PKCS#5 v2.1 be used instead.
o Addition of comments and minor corrections to the ASN.1 module in Appendix C.
o Removal of the export regulations discussion in the former Appendix D.
o Replacement of RSA with EMC in the "Intellectual Property Considerations".
o Many changes and additions to the references.
o A reference was added to NIST SP 800-132 for its recommendations on selection of the iteration count value for password integrity (part of dictionary-attack resistance).
o Comment included on acronym expansion of PFX: The acronym is sometimes expanded as Personal Information Exchange.
o In Appendix B, the phrase "no longer recommended" was changed to "not recommended" in the following sentence to address a question and make it clear the method was not recommended: "Note that this method for password privacy mode is no longer recommended."
AlgorithmIdentifier: An ASN.1 type that identifies an algorithm (by an object identifier) and any associated parameters. This type is defined in [8].
ASN.1: Abstract Syntax Notation One, as defined in [2], [3], [4], and [5].
Attribute: An ASN.1 type that identifies an attribute type (by an object identifier) and an associated attribute value. The ASN.1 type Attribute is defined in [7].
Certificate: A digitally signed data unit binding a public key to identity information. A specific format for identity certificates is defined in [8]. Another format is described in [17].
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Certificate Revocation List (CRL): A digitally signed list of certificates that should no longer be honored, having been revoked by the issuers or a higher authority. One format for CRLs is defined in [8].
ContentInfo: An ASN.1 type used to hold data that may have been cryptographically protected. This type is defined in [21] and [14].
DER: Distinguished Encoding Rules, as defined in [6].
Destination platform: The ultimate, final target platform for the personal information originating from the source platform. Even though certain information may be transported from the destination platform to the source platform, the ultimate target for personal information is always called the destination platform.
DigestInfo: An ASN.1 type used to hold a message digest. This type is defined in [21] and [14].
Encryption Key Pair (DestEncK): A public/private key pair used for the public-key privacy mode of this standard. The public half is called PDestEncK (TPDestEncK when emphasizing that the public key is "trusted"), and the private half is called VDestEncK.
Export time: The time that a user reads personal information from a source platform and transforms the information into an interoperable, secure Protocol Data Unit (PDU).
Import time: The time that a user writes personal information from a Safe PDU to a destination platform.
Message Authentication Code (MAC): A type of collision-resistant, "unpredictable" function of a message and a secret key. MACs are used for data authentication and are akin to secret-key digital signatures in many respects.
Object Identifier: A sequence of integers that uniquely identifies an associated data object in a global name space administrated by a hierarchy of naming authorities. This is a primitive data type in ASN.1.
PFX: The top-level exchange PDU defined in this standard. The acronym is sometimes expanded as Personal Information Exchange.
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Platform: A combination of machine, operating system, and applications software within which the user exercises personal identity. An application, in this context, is software that uses personal information. Two platforms differ if their machine types differ or if their applications software differs. There is at least one platform per user in multi-user systems.
Protocol Data Unit (PDU): A sequence of bits in machine-independent format constituting a message in a protocol.
Shrouding: Encryption as applied to private keys, possibly in concert with a policy that prevents the plaintext of the key from ever being visible beyond a certain, well-defined interface.
Signature Key Pair (SrcSigK): A platform-specific signature key pair used for the public-key integrity mode of this standard. The public half is called PSrcSigK (TPSrcSigK when emphasizing that the public key is "trusted"), and the private half is called VSrcSigK.
Source platform: The origin platform of the personal information ultimately intended for the destination platform. Even though certain information may be transported from the destination platform to the source platform, the platform that is the origin of personal information is always called the source platform.
There are four combinations of privacy modes and integrity modes. The privacy modes use encryption to protect personal information from exposure, and the integrity modes protect personal information from tampering. Without protection from tampering, an adversary could conceivably substitute invalid information for the user's personal information without the user being aware of the substitution.
The following are the privacy modes:
o Public-key privacy mode: Personal information is enveloped on the source platform using a trusted encryption public key of a known destination platform (see Section 3.3). The envelope is opened with the corresponding private key.
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o Password privacy mode: Personal information is encrypted with a symmetric key derived from a user name and a privacy password, as in [22] and [13]. If password integrity mode is used as well, the privacy password and the integrity password may or may not be the same.
The following are the integrity modes:
o Public-key integrity mode: Integrity is guaranteed through a digital signature on the contents of the PFX PDU, which is produced using the source platform's private signature key. The signature is verified on the destination platform by using the corresponding public key (see Section 3.4).
o Password integrity mode: Integrity is guaranteed through a Message Authentication Code (MAC) derived from a secret integrity password. If password privacy mode is used as well, the privacy password and the integrity password may or may not be the same.
All combinations of the privacy and integrity modes are permitted in this standard. Of course, good security policy suggests that certain practices be avoided, e.g., it can be unwise to transport private keys without physical protection when using password privacy mode or when using public-key privacy mode with weak symmetric encryption.
In general, the public-key modes for both privacy and integrity are preferable to the password modes (from a security viewpoint). However, it is not always possible to use the public-key modes. For example, it may not be known at export time what the destination platform is; if this is the case, then the use of the public-key privacy mode is precluded.
Asymmetric key pairs may be used in this standard in two ways: public-key privacy mode and public-key integrity mode. For public- key privacy mode, an encryption key pair is required; for public-key integrity mode, a signature key pair is required.
It may be appropriate for the keys discussed in this section to be platform-specific keys dedicated solely for the purpose of transporting a user's personal information. Whether or not that is the case, though, the keys discussed here should not be confused with the user's personal keys that the user wishes to transport from one platform to another. (These latter keys are stored within the PDU.)
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For public-key privacy mode, the private key from the encryption key pair is kept on the destination platform, where it is ultimately used to open a private envelope. The corresponding trusted public key is called TPDestEncK.
For public-key integrity mode, the private key from the signature pair is kept on the source platform, where it is used to sign personal information. The corresponding trusted public key is called TPSrcSigK.
For both uses of public/private key pairs, the public key from the key pair must be transported to the other platform such that it is trusted to have originated at the correct platform. Judging whether or not a public key is trusted in this sense must ultimately be left to the user. There are a variety of methods for ensuring that a public key is trusted.
The processes of imbuing keys with trust and of verifying trustworthiness of keys are not discussed further in this document. Whenever asymmetric keys are discussed in what follows, the public keys are assumed to be trusted.
Each compliant platform shall be able to import and export AuthenticatedSafe PDUs wrapped in PFX PDUs.
For integrity, the AuthenticatedSafe is either signed (if public-key integrity mode is used) or MACed (if password integrity mode is used) to produce a PFX PDU. If the AuthenticatedSafe is signed, then it is accompanied by a digital signature, which was produced on the source platform with a private signature key, VSrcSigK, corresponding to a trusted public signature key, TPSrcSigK. TPSrcSigK must accompany the PFX to the destination platform, where the user can verify the trust in the key and can verify the signature on the AuthenticatedSafe. If the AuthenticatedSafe is MACed, then it is accompanied by a MAC computed from a secret integrity password, salt bits, an iteration count, and the contents of the AuthenticatedSafe.
The AuthenticatedSafe itself consists of a sequence of ContentInfo values, some of which may consist of plaintext (data), and others that may either be enveloped (if public-key privacy mode is used) or encrypted (if password privacy mode is used). If the contents are enveloped, then they are encrypted with a symmetric cipher under a freshly generated key, which is in turn encrypted with RSA asymmetric encryption. The RSA public key used to encrypt the symmetric key is called TPDestEncK and corresponds to an RSA private key, VDestEncK, on the destination platform. TPDestEncK needs to be trusted by the
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user when it is used at export time. If the contents are encrypted, then they are encrypted with a symmetric cipher under a key derived from a secret privacy password, salt bits, and an iteration counter.
Each ContentInfo contains an arbitrary collection of private keys, PKCS #8-shrouded private keys, certificates, CRLs, or opaque data objects, at the user's discretion, stored in values of type SafeContents.
The raison d'etre for the unencrypted option is that some governments restrict certain uses of cryptography. Having several parts in an AuthenticatedSafe keeps implementers' options open. For example, it may be the case that strong cryptography can be used to make PKCS #8-shrouded keys, but then these shrouded keys should not be further encrypted, because super-encryption can limit a product's exportability. The multi-part AuthenticatedSafe design permits this possibility.
Around the AuthenticatedSafe is the integrity-mode wrapper, which protects the entire contents of the AuthenticatedSafe (including unencrypted parts, if they are present). This is the reverse of the wrapping order in many protocols, in which privacy is the outermost protection. This latter, more-common wrapping order avoids signatures on encrypted data, which are undesirable under certain circumstances; however, these circumstances do not apply to this document, and it is therefore preferable to protect the integrity of as much information as possible.
This format corresponds to the data model presented above, with wrappers for privacy and integrity. This section makes free reference to PKCS #7 [14] [21] and assumes the reader is familiar with terms defined in that document.
All modes of direct exchange use the same PDU format. ASN.1 and BER- encoding ensure platform independence.
This standard has one ASN.1 export: PFX. This is the outer integrity wrapper. Instances of PFX contain:
1. A version indicator. The version shall be v3 for this version of this document.
2. A PKCS #7 ContentInfo, whose contentType is signedData in public- key integrity mode and data in password integrity mode.
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3. An optional instance of MacData, present only in password integrity. This object, if present, contains a PKCS #7 DigestInfo, which holds the MAC value, a macSalt, and an iterationCount. As described in Appendix B, the MAC key is derived from the password, the macSalt, and the iterationCount; as described in Section 5, the MAC is computed from the authSafe value and the MAC key via HMAC [11] [20]. The password and the MAC key are not actually present anywhere in the PFX. The salt and (to a certain extent) the iteration count thwarts dictionary attacks against the integrity password. See NIST Special Publication 800-132 [12] about how to choose a reasonable value for the iteration count.
MacData ::= SEQUENCE { mac DigestInfo, macSalt OCTET STRING, iterations INTEGER DEFAULT 1 -- Note: The default is for historical reasons and its -- use is deprecated. }
As mentioned, the contentType field of authSafe shall be of type data or signedData. The content field of the authSafe shall, either directly (data case) or indirectly (signedData case), contain a BER- encoded value of type AuthenticatedSafe.
AuthenticatedSafe ::= SEQUENCE OF ContentInfo -- Data if unencrypted -- EncryptedData if password-encrypted -- EnvelopedData if public key-encrypted
An AuthenticatedSafe contains a sequence of ContentInfo values. The content field of these ContentInfo values contains either plaintext, encrypted, or enveloped data. In the case of encrypted or enveloped data, the plaintext of the data holds the BER-encoding of an instance of SafeContents. Section 5.1 of this document describes the construction of values of type AuthenticatedSafe in more detail.
The SafeContents type is made up of SafeBags. Each SafeBag holds one piece of information -- a key, a certificate, etc. -- which is identified by an object identifier.
SafeContents ::= SEQUENCE OF SafeBag
SafeBag ::= SEQUENCE { bagId BAG-TYPE.&id ({PKCS12BagSet}) bagValue [0] EXPLICIT BAG-TYPE.&Type({PKCS12BagSet}{@bagId}), bagAttributes SET OF PKCS12Attribute OPTIONAL }
PKCS12Attribute ::= SEQUENCE { attrId ATTRIBUTE.&id ({PKCS12AttrSet}), attrValues SET OF ATTRIBUTE.&Type ({PKCS12AttrSet}{@attrId}) } -- This type is compatible with the X.500 type 'Attribute'
PKCS12AttrSet ATTRIBUTE ::= { friendlyName | -- from PKCS #9 [23] localKeyId, -- from PKCS #9 ... -- Other attributes are allowed }
The optional bagAttributes field allows users to assign nicknames and identifiers to keys, etc., and permits visual tools to display meaningful strings of some sort to the user.
Six types of SafeBags are defined in this version of this document:
bagtypes OBJECT IDENTIFIER ::= {pkcs-12 10 1}
BAG-TYPE ::= TYPE-IDENTIFIER
keyBag BAG-TYPE ::= {KeyBag IDENTIFIED BY {bagtypes 1}} pkcs8ShroudedKeyBag BAG-TYPE ::= {PKCS8ShroudedKeyBag IDENTIFIED BY {bagtypes 2}} certBag BAG-TYPE ::= {CertBag IDENTIFIED BY {bagtypes 3}} crlBag BAG-TYPE ::= {CRLBag IDENTIFIED BY {bagtypes 4}} secretBag BAG-TYPE ::= {SecretBag IDENTIFIED BY {bagtypes 5}} safeContentsBag BAG-TYPE ::= {SafeContents IDENTIFIED BY {bagtypes 6}}
A PKCS8ShroudedKeyBag holds a private key, which has been shrouded in accordance with PKCS #8. Note that a PKCS8ShroudedKeyBag holds only one shrouded private key.
Each of the user's miscellaneous personal secrets is contained in an instance of SecretBag, which holds an object identifier-dependent value. Note that a SecretBag contains only one secret.
The sixth type of bag that can be held in a SafeBag is a SafeContents. This recursive structure allows for arbitrary nesting of multiple KeyBags, PKCS8ShroudedKeyBags, CertBags, CRLBags, and SecretBags within the top-level SafeContents.
1. It is somewhat clear from the ASN.1 how to make a number of instances of SafeContents, each containing a number of (possibly nested) instances of SafeBag. Let us assume, therefore, a number of instances SC_1, SC_2,..., SC_n of SafeContents. Note that there can be a more or less arbitrary number of instances of SafeContents in a PFX PDU. As will be seen in step 2, each instance can be encrypted (or not) separately.
2. For each SCI, depending on the chosen encryption option,
A. If SC_i is not to be encrypted, make a ContentInfo CI_i holding content type Data. The contents of the Data OCTET STRING shall be a BER-encoding of SC_i (including tag, length, and value octets).
B. If SC_i is to be encrypted with a password, make a ContentInfo CI_i of type EncryptedData. The encryptedContentInfo field of CI_i has its contentType field set to data and its encryptedContent field set to the encryption of the BER-encoding of SC_i (note that the tag and length octets shall be present).
C. If SC_i is to be encrypted with a public key, make a ContentInfo CI_i of type EnvelopedData in essentially the same fashion as the EncryptedData ContentInfo was made in B.
3. Make an instance of AuthenticatedSafe by stringing together the CI_i's in a SEQUENCE.
4. Make a ContentInfo T holding content type Data. The contents of the Data OCTET STRING shall be a BER-encoding of the AuthenticatedSafe value (including tag, length, and value octets).
5. For integrity protection,
A. If the PFX PDU is to be authenticated with a digital signature, make a ContentInfo C of type SignedData. The contentInfo field of the SignedData in C has T in it. C is the ContentInfo in the top-level PFX structure.
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B. If the PFX PDU is to be authenticated with HMAC, then an HMAC with SHA-1, SHA-224, SHA-256, SHA-384, SHA-512, SHA-512/224, or SHA-512/256 is computed on the contents of the Data in T (i.e., excluding the OCTET STRING tag and length bytes). This is exactly what would be initially digested in step 5A if public-key authentication were being used.
Importation from a PFX is accomplished essentially by reversing the procedure for creating a PFX. In general, when an application imports keys, etc., from a PFX, it should ignore any object identifiers that it is not familiar with. At times, it may be appropriate to alert the user to the presence of such object identifiers.
Special care may be taken by the application when importing an item in the PFX would require overwriting an item that already exists locally. The behavior of the application when such an item is encountered may depend on what the item is (i.e., it may be that a PKCS #8-shrouded private key and a CRL should be treated differently here). Appropriate behavior may be to ask the user what action should be taken for this item.
When using passwords in privacy or integrity mode, it needs to be considered that password-based cryptography is generally limited in the security that it can provide, particularly for methods such as those defined in this document where off-line password search is possible. While the use of salt and iteration count can increase the complexity of attack, it is essential that passwords are selected well and that relevant guidelines (e.g., NIST SP 800-61-1) are taken into account. It is also important that passwords be protected well if stored.
When choosing a salt value in password privacy or integrity mode, the recommendations in Section 4 of PKCS #5 2.1 [13] [22] should be taken into account. Ideally, the salt is as long as the output of the hash function being used and consists of randomly generated data.
[7] ISO/IEC, "Information technology -- Open Systems Interconnection -- The Directory: Models", ISO/IEC 9594-2:1997, 1997.
[8] ISO/IEC, "Information technology -- Open Systems Interconnection -- The Directory: Authentication Framework", ISO/IEC 9594-8:1997, 1997.
[9] Microsoft, "PFX: Personal Exchange Syntax and Protocol Standard", ISO/IEC Version 0.020, January 1997.
[10] National Institute of Standards and Technology (NIST), "Secure Hash Standard", FIPS Publication 180-4, March 2012.
[11] National Institute of Standards and Technology (NIST), "The Keyed-Hash Message Authentication Code (HMAC)", FIPS Publication 198-1, July 2008.
[12] National Institute of Standards and Technology (NIST), "The Recommendation for Password-Based Key Derivation, Part 1: Storage Applications", NIST Special Publication 800-132, December 2010.
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[13] RSA Laboratories, "PKCS #5: Password-Based Encryption Standard", PKCS Version 2.1, October 2012.
[14] RSA Laboratories, "PKCS #7: Cryptographic Message Syntax Standard", PKCS Version 1.5, November 1993.
[15] RSA Laboratories, "PKCS #8: Private-Key Information Syntax Standard", PKCS Version 1.2, November 1993.
[16] RSA Laboratories, "PKCS #12: Personal Information Exchange Syntax", PKCS Version 1.1, December 2012.
A MAC is a special type of function of a message (data bits) and an integrity key. It can be computed or checked only by someone possessing both the message and the integrity key. Its security follows from the secrecy of the integrity key. In this standard, MACing is used in password integrity mode.
This document uses a particular type of MAC called HMAC [11] [20], which can be constructed from any of a variety of hash functions. Note that the specifications in [20] and [11] differ somewhat from the specification in [9]. The hash function HMAC is based on is identified in the MacData, which holds the MAC; for this version of this standard, the hash function can be one of the following: SHA-1, SHA-224, SHA-256, SHA-384, SHA-512, SHA-512/224, or SHA-512/256 [10]. As indicated in Appendix B.4, this structure implies that the same hash algorithm must be used to derive the MAC key itself in password integrity mode and that the MAC key has either 160, 224, 256, 384, or 512 bits.
When password integrity mode is used to secure a PFX PDU, an HMAC with SHA-1, SHA-224, SHA-256, SHA-384, SHA-512, SHA-512/224, or SHA-512/256 is computed on the BER-encoding of the contents of the content field of the authSafe field in the PFX PDU (see Section 5.1).
Appendix B. Deriving Keys and IVs from Passwords and Salt
Note that this method for password privacy mode is not recommended and is deprecated for new usage. The procedures and algorithms defined in PKCS #5 v2.1 [13] [22] should be used instead. Specifically, PBES2 should be used as encryption scheme, with PBKDF2 as the key derivation function.
The method presented here is still used to generate the key in password integrity mode.
We present here a general method for using a hash function to produce various types of pseudorandom bits from a password and a string of salt bits. This method is used for password privacy mode and password integrity mode in the present standard.
The underlying password-based encryption methods in PKCS #5 v2.1 view passwords (and salt) as being simple byte strings. The underlying password-based encryption methods and the underlying password-based authentication methods in this version of this document are similar.
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What's left unspecified in the above paragraph is precisely where the byte string representing a password comes from. (This is not an issue with salt strings, since they are supplied as a password-based encryption (or authentication) parameter.) PKCS #5 v2.1 says: "[...] a password is considered to be an octet string of arbitrary length whose interpretation as a text string is unspecified. In the interest of interoperability, however, it is recommended that applications follow some common text encoding rules. ASCII and UTF-8 are two possibilities."
In this specification, however, all passwords are created from BMPStrings with a NULL terminator. This means that each character in the original BMPString is encoded in 2 bytes in big-endian format (most-significant byte first). There are no Unicode byte order marks. The 2 bytes produced from the last character in the BMPString are followed by 2 additional bytes with the value 0x00.
To illustrate with a simple example, if a user enters the 6-character password "Beavis", the string that PKCS #12 implementations should treat as the password is the following string of 14 bytes:
Let H be a hash function built around a compression function f:
Z_2^u x Z_2^v -> Z_2^u
(that is, H has a chaining variable and output of length u bits, and the message input to the compression function of H is v bits). The values for u and v are as follows:
HASH FUNCTION VALUE u VALUE v MD2, MD5 128 512 SHA-1 160 512 SHA-224 224 512 SHA-256 256 512 SHA-384 384 1024 SHA-512 512 1024 SHA-512/224 224 1024 SHA-512/256 256 1024
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Furthermore, let r be the iteration count.
We assume here that u and v are both multiples of 8, as are the lengths of the password and salt strings (which we denote by p and s, respectively) and the number n of pseudorandom bits required. In addition, u and v are of course non-zero.
For information on security considerations for MD5 [19], see [25] and [1], and on those for MD2, see [18].
The following procedure can be used to produce pseudorandom bits for a particular "purpose" that is identified by a byte called "ID". The meaning of this ID byte will be discussed later.
1. Construct a string, D (the "diversifier"), by concatenating v/8 copies of ID.
2. Concatenate copies of the salt together to create a string S of length v(ceiling(s/v)) bits (the final copy of the salt may be truncated to create S). Note that if the salt is the empty string, then so is S.
3. Concatenate copies of the password together to create a string P of length v(ceiling(p/v)) bits (the final copy of the password may be truncated to create P). Note that if the password is the empty string, then so is P.
4. Set I=S||P to be the concatenation of S and P.
5. Set c=ceiling(n/u).
6. For i=1, 2, ..., c, do the following:
A. Set A2=H^r(D||I). (i.e., the r-th hash of D||1, H(H(H(... H(D||I))))
B. Concatenate copies of Ai to create a string B of length v bits (the final copy of Ai may be truncated to create B).
C. Treating I as a concatenation I_0, I_1, ..., I_(k-1) of v-bit blocks, where k=ceiling(s/v)+ceiling(p/v), modify I by setting I_j=(I_j+B+1) mod 2^v for each j.
7. Concatenate A_1, A_2, ..., A_c together to form a pseudorandom bit string, A.
8. Use the first n bits of A as the output of this entire process.
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If the above process is being used to generate a DES key, the process should be used to create 64 random bits, and the key's parity bits should be set after the 64 bits have been produced. Similar concerns hold for 2-key and 3-key triple-DES keys, for CDMF keys, and for any similar keys with parity bits "built into them".
When password integrity mode is used to protect a PFX PDU, a password and salt are used to derive a MAC key. As with password privacy mode, the password is a Unicode string, and the salt is a byte string. No particular lengths are prescribed in this standard for either the password or the salt, but the general advice about passwords and salt that is given in Appendix C applies here, as well.
The hash function used to derive MAC keys is whatever hash function is going to be used for MACing. The MAC keys that are derived have the same length as the hash function's output. In this version of this standard, SHA-1, SHA-224, SHA-256, SHA384, SHA-512, SHA-512/224, or SHA/512/256 can be used to perform MACing, and so the MAC keys can be 160, 224, 256, 384, or 512 bits. See Appendix A for more information on MACing.
Appendix C. Keys and IVs for Password Privacy Mode
As stated at the start of Appendix B, use of this method for password privacy mode is not recommended; this specification of keys and IVs for password privacy mode is retained for backwards compatibility with PKCS #12 v1.0 only.
When password privacy mode is used to encrypt a PFX PDU, a password (typically entered by the user), a salt and an iteration parameter are used to derive a key (and an IV, if necessary). The password is
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a Unicode string, and as such, each character in it is represented by 2 bytes. The salt is a byte string and so can be represented directly as a sequence of bytes.
This standard does not prescribe a length for the password. As usual, however, too short a password might compromise privacy. A particular application might well require a user-entered privacy password for creating a PFX PDU to have a password exceeding some specific length.
This standard does not prescribe a length for the salt either. Ideally, the salt is as long as the output of the hash function being used and consists of completely random bits.
The iteration count is recommended to be 1024 or more. (See [22] and [13] for more information.)
The PBES1 encryption scheme defined in PKCS #5 provides a number of algorithm identifiers for deriving keys and IVs; here, we specify a few more, all of which use the procedure detailed in Appendices B.2 and B.3 to construct keys (and IVs, where needed). As is implied by their names, all of the object identifiers below use the hash function SHA-1.
Each of the six PBE object identifiers above has the following ASN.1 type for parameters:
pkcs-12PbeParams ::= SEQUENCE { salt OCTET STRING, iterations INTEGER }
The pkcs-12PbeParams holds the salt that is used to generate the key (and IV, if necessary) and the number of iterations to carry out.
Note that the first two algorithm identifiers above (the algorithm identifiers for RC4) only derive keys; it is unnecessary to derive an IV for RC4.
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This section is here for two reasons: first, to enable backwards compatibility as described in the first paragraph of this section; second, because it is still used in password integrity mode. In order to not use it in password integrity mode, the ASN.1 definitions require updates. This document recommends that future definitions of the PFX structure replace the existing MacData object, optionally present in password integrity mode, with a new object definition that holds a MAC based on PKCS#5 [13] [22] PBMAC1 message authentication scheme. This change would simplify the requirements for key derivation functions used across all parts of the PFX structure.
This appendix documents all ASN.1 types, values, and object sets defined in this specification. It does so by providing an ASN.1 module called PKCS-12.
MacData ::= SEQUENCE { mac DigestInfo, macSalt OCTET STRING, iterations INTEGER DEFAULT 1 -- Note: The default is for historical reasons and its use is -- deprecated. }
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AuthenticatedSafe ::= SEQUENCE OF ContentInfo -- Data if unencrypted -- EncryptedData if password-encrypted -- EnvelopedData if public key-encrypted
SafeContents ::= SEQUENCE OF SafeBag
SafeBag ::= SEQUENCE { bagId BAG-TYPE.&id ({PKCS12BagSet}), bagValue [0] EXPLICIT BAG-TYPE.&Type({PKCS12BagSet}{@bagId}), bagAttributes SET OF PKCS12Attribute OPTIONAL }
-- ============================ -- Bag types -- ============================
keyBag BAG-TYPE ::= {KeyBag IDENTIFIED BY {bagtypes 1}} pkcs8ShroudedKeyBag BAG-TYPE ::= {PKCS8ShroudedKeyBag IDENTIFIED BY {bagtypes 2}} certBag BAG-TYPE ::= {CertBag IDENTIFIED BY {bagtypes 3}} crlBag BAG-TYPE ::= {CRLBag IDENTIFIED BY {bagtypes 4}} secretBag BAG-TYPE ::= {SecretBag IDENTIFIED BY {bagtypes 5}} safeContentsBag BAG-TYPE ::= {SafeContents IDENTIFIED BY {bagtypes 6}}
PKCS12Attribute ::= SEQUENCE { attrId ATTRIBUTE.&id ({PKCS12AttrSet}), attrValues SET OF ATTRIBUTE.&Type ({PKCS12AttrSet}{@attrId}) } -- This type is compatible with the X.500 type 'Attribute'
PKCS12AttrSet ATTRIBUTE ::= { friendlyName | localKeyId, ... -- Other attributes are allowed }
EMC Corporation makes no patent claims on the general constructions described in this document, although specific underlying techniques may be covered.
RC2 and RC4 are trademarks of EMC Corporation.
EMC Corporation makes no representations regarding intellectual property claims by other parties. Such determination is the responsibility of the user.
Many thanks to Dan Simon of Microsoft Corporation and Jim Spring of Netscape Communications Corporation for their assistance in preparing early drafts of this document. Especial thanks to Brian Beckman of Microsoft Corporation for writing the specification that this document is based on.
The Public-Key Cryptography Standards are specifications produced by RSA Laboratories in cooperation with secure systems developers worldwide for the purpose of accelerating the deployment of public- key cryptography. First published in 1991 as a result of meetings with a small group of early adopters of public-key technology, the PKCS documents have become widely referenced and implemented. Contributions from the PKCS series have become part of many formal and de facto standards, including ANSI X9 documents, PKIX, SET, S/ MIME, and SSL.
Further development of PKCS occurs through the IETF. Suggestions for improvement are welcome.
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Authors' Addresses
Kathleen M. Moriarty (editor) EMC Corporation 176 South Street Hopkinton, MA United States
EMail: Kathleen.Moriarty@emc.com
Magnus Nystrom Microsoft Corporation 1 Microsoft Way Redmond, WA 98052 United States
EMail: mnystrom@microsoft.com
Sean Parkinson RSA Security Inc. 345 Queen Street Brisbane, QLD, 4000 Australia
EMail: Sean.Parkinson@rsa.com
Andreas Rusch RSA Security Inc. 345 Queen Street Brisbane, QLD, 4000 Australia
EMail: Andreas.Rusch@rsa.com
Michael Scott RSA Security Inc. 345 Queen Street Brisbane, QLD, 4000 Australia