Difference between revisions of "RFC5959"
Line 10: | Line 10: | ||
This document describes the conventions for using several | This document describes the conventions for using several | ||
cryptographic algorithms with the EncryptedPrivateKeyInfo structure, | cryptographic algorithms with the EncryptedPrivateKeyInfo structure, | ||
− | as defined in RFC 5958. It also includes conventions necessary to | + | as defined in [[RFC5958|RFC 5958]]. It also includes conventions necessary to |
protect the AsymmetricKeyPackage content type with SignedData, | protect the AsymmetricKeyPackage content type with SignedData, | ||
EnvelopedData, EncryptedData, AuthenticatedData, and | EnvelopedData, EncryptedData, AuthenticatedData, and | ||
Line 23: | Line 23: | ||
received public review and has been approved for publication by the | received public review and has been approved for publication by the | ||
Internet Engineering Steering Group (IESG). Further information on | Internet Engineering Steering Group (IESG). Further information on | ||
− | Internet Standards is available in Section 2 of RFC 5741. | + | Internet Standards is available in Section 2 of [[RFC5741|RFC 5741]]. |
Information about the current status of this document, any errata, | Information about the current status of this document, any errata, | ||
Line 34: | Line 34: | ||
document authors. All rights reserved. | document authors. All rights reserved. | ||
− | This document is subject to BCP 78 and the IETF Trust's Legal | + | This document is subject to [[BCP78|BCP 78]] and the IETF Trust's Legal |
Provisions Relating to IETF Documents | Provisions Relating to IETF Documents | ||
(http://trustee.ietf.org/license-info) in effect on the date of | (http://trustee.ietf.org/license-info) in effect on the date of | ||
Line 48: | Line 48: | ||
This document describes the conventions for using several | This document describes the conventions for using several | ||
cryptographic algorithms with the EncryptedPrivateKeyInfo structure | cryptographic algorithms with the EncryptedPrivateKeyInfo structure | ||
− | + | [[RFC5958]]. The EncryptedPrivateKeyInfo is used by [P12] to encrypt | |
− | PrivateKeyInfo | + | PrivateKeyInfo [[RFC5958]]. It is similar to EncryptedData [[RFC5652]] |
in that it has no recipients, no originators, and no content | in that it has no recipients, no originators, and no content | ||
encryption keys and requires keys to be managed by other means. | encryption keys and requires keys to be managed by other means. | ||
This document also includes conventions necessary to protect the | This document also includes conventions necessary to protect the | ||
− | AsymmetricKeyPackage content type | + | AsymmetricKeyPackage content type [[RFC5958]] with Cryptographic |
− | Message Syntax (CMS) protecting content types: SignedData | + | Message Syntax (CMS) protecting content types: SignedData [[RFC5652]], |
− | EnvelopedData | + | EnvelopedData [[RFC5652]], EncryptedData [[RFC5652]], AuthenticatedData |
− | + | [[RFC5652]], and AuthEnvelopedData [[RFC5083]]. Implementations of | |
AsymmetricKeyPackage do not require support for any CMS protecting | AsymmetricKeyPackage do not require support for any CMS protecting | ||
content type; however, if the AsymmetricKeyPackage is CMS protected | content type; however, if the AsymmetricKeyPackage is CMS protected | ||
Line 69: | Line 69: | ||
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", | The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", | ||
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this | "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this | ||
− | document are to be interpreted as described in | + | document are to be interpreted as described in [[RFC2119]]. |
== EncryptedPrivateKeyInfo == | == EncryptedPrivateKeyInfo == | ||
Line 76: | Line 76: | ||
which is subsequently placed in the EncryptedPrivateKeyInfo | which is subsequently placed in the EncryptedPrivateKeyInfo | ||
encryptedData field, is Password Based Encryption (PBE) based on PKCS | encryptedData field, is Password Based Encryption (PBE) based on PKCS | ||
− | #5 | + | #5 [[RFC2898]] and PKCS #12 [P12]. The major difference between PKCS |
#5 and PKCS #12 is the supported encoding for the password: ASCII for | #5 and PKCS #12 is the supported encoding for the password: ASCII for | ||
PKCS #5 and Unicode for PKCS #12, encoded as specified in Section B.1 | PKCS #5 and Unicode for PKCS #12, encoded as specified in Section B.1 | ||
− | of [P12]. | + | of [P12]. [[RFC2898]] specifies two PBE Schemes (PBES) 1 and 2; |
− | + | [[RFC2898]] recommends PBES2 for new specification. PBES2 with a key | |
− | derivation algorithm of PBKDF2 using HMAC with SHA-256 | + | derivation algorithm of PBKDF2 using HMAC with SHA-256 [[RFC5754]] and |
an encryption algorithm of AES Key Wrap with Padding as defined in | an encryption algorithm of AES Key Wrap with Padding as defined in | ||
− | + | [[RFC5649]] MUST be supported. AES-256 Key Wrap with Padding [[RFC5649]] | |
MAY also be supported as an encryption algorithm. | MAY also be supported as an encryption algorithm. | ||
== AsymmetricKeyPackage == | == AsymmetricKeyPackage == | ||
− | As noted in Asymmetric Key Packages | + | As noted in Asymmetric Key Packages [[RFC5958]], CMS can be used to |
protect the AsymmetricKeyPackage. The following provides guidance | protect the AsymmetricKeyPackage. The following provides guidance | ||
− | for SignedData | + | for SignedData [[RFC5652]], EnvelopedData [[RFC5652]], EncryptedData |
− | + | [[RFC5652]], AuthenticatedData [[RFC5652]], and AuthEnvelopedData | |
− | + | [[RFC5083]]. | |
=== SignedData === | === SignedData === | ||
If an implementation supports SignedData, then it MUST support the | If an implementation supports SignedData, then it MUST support the | ||
− | signature scheme RSA | + | signature scheme RSA [[RFC3370]] [[RFC5754]] and SHOULD support the |
− | signature schemes RSASSA-PSS | + | signature schemes RSASSA-PSS [[RFC4056]] and DSA [[RFC3370]] [[RFC5754]]. |
Additionally, implementations MUST support in concert with these | Additionally, implementations MUST support in concert with these | ||
− | signature schemes the hash function SHA-256 | + | signature schemes the hash function SHA-256 [[RFC5754]] and SHOULD |
− | support the hash function SHA-1 | + | support the hash function SHA-1 [[RFC3370]]. |
=== EnvelopedData === | === EnvelopedData === | ||
Line 109: | Line 109: | ||
key transport and it MAY implement key agreement. | key transport and it MAY implement key agreement. | ||
− | When key transport is used, RSA encryption | + | When key transport is used, RSA encryption [[RFC3370]] MUST be |
supported and RSAES-OAEP (RSA Encryption Scheme - Optimal Asymmetric | supported and RSAES-OAEP (RSA Encryption Scheme - Optimal Asymmetric | ||
− | Encryption Padding) | + | Encryption Padding) [[RFC3560]] SHOULD be supported. |
When key agreement is used, Diffie-Hellman (DH) ephemeral-static | When key agreement is used, Diffie-Hellman (DH) ephemeral-static | ||
− | + | [[RFC3370]] MUST be supported. | |
Since the content type is used to carry a cryptographic key and its | Since the content type is used to carry a cryptographic key and its | ||
Line 120: | Line 120: | ||
key with another is employed. Regardless of the key management | key with another is employed. Regardless of the key management | ||
technique choice, implementations MUST support AES-128 Key Wrap with | technique choice, implementations MUST support AES-128 Key Wrap with | ||
− | Padding | + | Padding [[RFC5649]] as the content encryption algorithm. |
Implementations SHOULD support AES-256 Key Wrap with Padding | Implementations SHOULD support AES-256 Key Wrap with Padding | ||
− | + | [[RFC5649]] as the content encryption algorithm. | |
When key agreement is used, a key wrap algorithm is also specified to | When key agreement is used, a key wrap algorithm is also specified to | ||
wrap the content encryption key. If the content encryption algorithm | wrap the content encryption key. If the content encryption algorithm | ||
is AES-128 Key Wrap with Padding, then the key wrap algorithm MUST be | is AES-128 Key Wrap with Padding, then the key wrap algorithm MUST be | ||
− | AES-128 Key Wrap with Padding | + | AES-128 Key Wrap with Padding [[RFC5649]]. If the content encryption |
algorithm is AES-256 Key Wrap with Padding, then the key wrap | algorithm is AES-256 Key Wrap with Padding, then the key wrap | ||
− | algorithm MUST be AES-256 Key Wrap with Padding | + | algorithm MUST be AES-256 Key Wrap with Padding [[RFC5649]]. |
=== EncryptedData === | === EncryptedData === | ||
If an implementation supports EncryptedData, then it MUST implement | If an implementation supports EncryptedData, then it MUST implement | ||
− | AES-128 Key Wrap with Padding | + | AES-128 Key Wrap with Padding [[RFC5649]] and SHOULD implement AES-256 |
− | Key Wrap with Padding | + | Key Wrap with Padding [[RFC5649]]. |
NOTE: EncryptedData requires that keys be managed by other means; | NOTE: EncryptedData requires that keys be managed by other means; | ||
Line 146: | Line 146: | ||
If an implementation supports AuthenticatedData, then it MUST | If an implementation supports AuthenticatedData, then it MUST | ||
− | implement SHA-256 | + | implement SHA-256 [[RFC5754]] and SHOULD support SHA-1 [[RFC3370]] as the |
− | message digest algorithm. Additionally, HMAC with SHA-256 | + | message digest algorithm. Additionally, HMAC with SHA-256 [[RFC4231]] |
− | MUST be supported and HMAC with SHA-1 | + | MUST be supported and HMAC with SHA-1 [[RFC3370]] SHOULD be supported. |
=== AuthEnvelopedData === | === AuthEnvelopedData === | ||
Line 154: | Line 154: | ||
If an implementation supports AuthEnvelopedData, then it MUST | If an implementation supports AuthEnvelopedData, then it MUST | ||
implement the EnvelopedData recommendations except for the content | implement the EnvelopedData recommendations except for the content | ||
− | encryption algorithm, which in this case MUST be AES-GCM | + | encryption algorithm, which in this case MUST be AES-GCM [[RFC5084]]; |
the 128-bit version MUST be implemented and the 256-bit version | the 128-bit version MUST be implemented and the 256-bit version | ||
SHOULD be implemented. Implementations MAY also support for AES-CCM | SHOULD be implemented. Implementations MAY also support for AES-CCM | ||
− | + | [[RFC5084]]. | |
== Public Key Sizes == | == Public Key Sizes == | ||
The easiest way to implement the SignedData, EnvelopedData, and | The easiest way to implement the SignedData, EnvelopedData, and | ||
− | AuthEnvelopedData is with public key certificates | + | AuthEnvelopedData is with public key certificates [[RFC5280]]. If an |
implementation support RSA, RSASSA-PSS, DSS, RSAES-OAEP, or DH, then | implementation support RSA, RSASSA-PSS, DSS, RSAES-OAEP, or DH, then | ||
it MUST support key lengths from 1024-bit to 2048-bit, inclusive. | it MUST support key lengths from 1024-bit to 2048-bit, inclusive. | ||
Line 168: | Line 168: | ||
== SMIMECapabilities Attribute == | == SMIMECapabilities Attribute == | ||
− | + | [[RFC5751]] defines the SMIMECapabilities attribute as a mechanism for | |
recipients to indicate their supported capabilities including the | recipients to indicate their supported capabilities including the | ||
algorithms they support. The following are values for the | algorithms they support. The following are values for the | ||
− | SMIMECapabilities attribute for AES Key Wrap with Padding | + | SMIMECapabilities attribute for AES Key Wrap with Padding [[RFC5649]] |
when used as a content encryption algorithm: | when used as a content encryption algorithm: | ||
Line 180: | Line 180: | ||
== Security Considerations == | == Security Considerations == | ||
− | The security considerations from | + | The security considerations from [[RFC3370]], [[RFC3560]], [[RFC4056]], |
− | + | [[RFC4231]], [[RFC5083]], [[RFC5084]], [[RFC5649]], [[RFC5652]], [[RFC5754]], and | |
− | + | [[RFC5958]] apply. | |
The strength of any encryption scheme is only as good as its weakest | The strength of any encryption scheme is only as good as its weakest | ||
Line 198: | Line 198: | ||
The choice of content encryption algorithms for this document was | The choice of content encryption algorithms for this document was | ||
− | based on | + | based on [[RFC5649]]: "In the design of some high assurance |
cryptographic modules, it is desirable to segregate cryptographic | cryptographic modules, it is desirable to segregate cryptographic | ||
keying material from other data. The use of a specific cryptographic | keying material from other data. The use of a specific cryptographic | ||
Line 219: | Line 219: | ||
Exchange Syntax", June 1999. | Exchange Syntax", June 1999. | ||
− | + | [[RFC2119]] Bradner, S., "Key words for use in RFCs to Indicate | |
− | Requirement Levels", BCP 14, RFC 2119, March 1997. | + | Requirement Levels", [[BCP14|BCP 14]], [[RFC2119|RFC 2119]], March 1997. |
− | + | [[RFC2898]] Kaliski, B., "PKCS #5: Password-Based Cryptography | |
− | Specification Version 2.0", RFC 2898, September 2000. | + | Specification Version 2.0", [[RFC2898|RFC 2898]], September 2000. |
− | + | [[RFC3370]] Housley, R., "Cryptographic Message Syntax (CMS) | |
− | Algorithms", RFC 3370, August 2002. | + | Algorithms", [[RFC3370|RFC 3370]], August 2002. |
− | + | [[RFC3560]] Housley, R., "Use of the RSAES-OAEP Key Transport | |
Algorithm in Cryptographic Message Syntax (CMS)", RFC | Algorithm in Cryptographic Message Syntax (CMS)", RFC | ||
3560, July 2003. | 3560, July 2003. | ||
− | + | [[RFC4056]] Schaad, J., "Use of the RSASSA-PSS Signature Algorithm in | |
− | Cryptographic Message Syntax (CMS)", RFC 4056, June 2005. | + | Cryptographic Message Syntax (CMS)", [[RFC4056|RFC 4056]], June 2005. |
− | + | [[RFC4231]] Nystrom, M., "Identifiers and Test Vectors for HMAC- | |
SHA-224, HMAC-SHA-256, HMAC-SHA-384, and HMAC-SHA-512", | SHA-224, HMAC-SHA-256, HMAC-SHA-384, and HMAC-SHA-512", | ||
− | RFC 4231, December 2005. | + | [[RFC4231|RFC 4231]], December 2005. |
− | + | [[RFC5083]] Housley, R., "Cryptographic Message Syntax (CMS) | |
− | Authenticated-Enveloped-Data Content Type", RFC 5083, | + | Authenticated-Enveloped-Data Content Type", [[RFC5083|RFC 5083]], |
November 2007. | November 2007. | ||
− | + | [[RFC5084]] Housley, R., "Using AES-CCM and AES-GCM Authenticated | |
Encryption in the Cryptographic Message Syntax (CMS)", | Encryption in the Cryptographic Message Syntax (CMS)", | ||
− | RFC 5084, November 2007. | + | [[RFC5084|RFC 5084]], November 2007. |
− | + | [[RFC5280]] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., | |
Housley, R., and W. Polk, "Internet X.509 Public Key | Housley, R., and W. Polk, "Internet X.509 Public Key | ||
Infrastructure Certificate and Certificate Revocation | Infrastructure Certificate and Certificate Revocation | ||
− | List (CRL) Profile", RFC 5280, May 2008. | + | List (CRL) Profile", [[RFC5280|RFC 5280]], May 2008. |
− | + | [[RFC5649]] Housley, R. and M. Dworkin, "Advanced Encryption Standard | |
− | (AES) Key Wrap with Padding Algorithm", RFC 5649, | + | (AES) Key Wrap with Padding Algorithm", [[RFC5649|RFC 5649]], |
September 2009. | September 2009. | ||
− | + | [[RFC5652]] Housley, R., "Cryptographic Message Syntax (CMS)", STD | |
− | 70, RFC 5652, September 2009. | + | 70, [[RFC5652|RFC 5652]], September 2009. |
− | + | [[RFC5751]] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet | |
Mail Extensions (S/MIME) Version 3.2 Message | Mail Extensions (S/MIME) Version 3.2 Message | ||
− | Specification", RFC 5751, January 2010. | + | Specification", [[RFC5751|RFC 5751]], January 2010. |
− | + | [[RFC5754]] Turner, S., "Using SHA2 Algorithms with Cryptographic | |
− | Message Syntax", RFC 5754, January 2010. | + | Message Syntax", [[RFC5754|RFC 5754]], January 2010. |
− | + | [[RFC5958]] Turner, S., "Asymmetric Key Packages", [[RFC5958|RFC 5958]], August | |
2010. | 2010. | ||
Latest revision as of 00:44, 22 October 2020
Internet Engineering Task Force (IETF) S. Turner Request for Comments: 5959 IECA Category: Standards Track August 2010 ISSN: 2070-1721
Algorithms for Asymmetric Key Package Content Type
Abstract
This document describes the conventions for using several cryptographic algorithms with the EncryptedPrivateKeyInfo structure, as defined in RFC 5958. It also includes conventions necessary to protect the AsymmetricKeyPackage content type with SignedData, EnvelopedData, EncryptedData, AuthenticatedData, and AuthEnvelopedData.
Status of This Memo
This is an Internet Standards Track document.
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). Further information on Internet Standards is available in 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/rfc5959.
Copyright Notice
Copyright (c) 2010 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.
Contents
Introduction
This document describes the conventions for using several cryptographic algorithms with the EncryptedPrivateKeyInfo structure RFC5958. The EncryptedPrivateKeyInfo is used by [P12] to encrypt PrivateKeyInfo RFC5958. It is similar to EncryptedData RFC5652 in that it has no recipients, no originators, and no content encryption keys and requires keys to be managed by other means.
This document also includes conventions necessary to protect the AsymmetricKeyPackage content type RFC5958 with Cryptographic Message Syntax (CMS) protecting content types: SignedData RFC5652, EnvelopedData RFC5652, EncryptedData RFC5652, AuthenticatedData RFC5652, and AuthEnvelopedData RFC5083. Implementations of AsymmetricKeyPackage do not require support for any CMS protecting content type; however, if the AsymmetricKeyPackage is CMS protected it is RECOMMENDED that conventions defined herein be followed.
This document does not define any new algorithms instead it refers to previously defined algorithms.
Terminology
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.
EncryptedPrivateKeyInfo
The de facto standard used to encrypt the PrivateKeyInfo structure, which is subsequently placed in the EncryptedPrivateKeyInfo encryptedData field, is Password Based Encryption (PBE) based on PKCS
- 5 RFC2898 and PKCS #12 [P12]. The major difference between PKCS
- 5 and PKCS #12 is the supported encoding for the password: ASCII for
PKCS #5 and Unicode for PKCS #12, encoded as specified in Section B.1 of [P12]. RFC2898 specifies two PBE Schemes (PBES) 1 and 2; RFC2898 recommends PBES2 for new specification. PBES2 with a key derivation algorithm of PBKDF2 using HMAC with SHA-256 RFC5754 and an encryption algorithm of AES Key Wrap with Padding as defined in RFC5649 MUST be supported. AES-256 Key Wrap with Padding RFC5649 MAY also be supported as an encryption algorithm.
AsymmetricKeyPackage
As noted in Asymmetric Key Packages RFC5958, CMS can be used to protect the AsymmetricKeyPackage. The following provides guidance for SignedData RFC5652, EnvelopedData RFC5652, EncryptedData
RFC5652, AuthenticatedData RFC5652, and AuthEnvelopedData RFC5083.
SignedData
If an implementation supports SignedData, then it MUST support the signature scheme RSA RFC3370 RFC5754 and SHOULD support the signature schemes RSASSA-PSS RFC4056 and DSA RFC3370 RFC5754. Additionally, implementations MUST support in concert with these signature schemes the hash function SHA-256 RFC5754 and SHOULD support the hash function SHA-1 RFC3370.
EnvelopedData
If an implementation supports EnvelopedData, then it MUST implement key transport and it MAY implement key agreement.
When key transport is used, RSA encryption RFC3370 MUST be supported and RSAES-OAEP (RSA Encryption Scheme - Optimal Asymmetric Encryption Padding) RFC3560 SHOULD be supported.
When key agreement is used, Diffie-Hellman (DH) ephemeral-static RFC3370 MUST be supported.
Since the content type is used to carry a cryptographic key and its attributes, an algorithm that is traditionally used to encrypt one key with another is employed. Regardless of the key management technique choice, implementations MUST support AES-128 Key Wrap with Padding RFC5649 as the content encryption algorithm. Implementations SHOULD support AES-256 Key Wrap with Padding RFC5649 as the content encryption algorithm.
When key agreement is used, a key wrap algorithm is also specified to wrap the content encryption key. If the content encryption algorithm is AES-128 Key Wrap with Padding, then the key wrap algorithm MUST be AES-128 Key Wrap with Padding RFC5649. If the content encryption algorithm is AES-256 Key Wrap with Padding, then the key wrap algorithm MUST be AES-256 Key Wrap with Padding RFC5649.
EncryptedData
If an implementation supports EncryptedData, then it MUST implement AES-128 Key Wrap with Padding RFC5649 and SHOULD implement AES-256 Key Wrap with Padding RFC5649.
NOTE: EncryptedData requires that keys be managed by other means; therefore, the only algorithm specified is the content encryption algorithm. Since the content type is used to carry a cryptographic key and its attributes, an algorithm that is traditionally used to encrypt one key with another is employed.
AuthenticatedData
If an implementation supports AuthenticatedData, then it MUST implement SHA-256 RFC5754 and SHOULD support SHA-1 RFC3370 as the message digest algorithm. Additionally, HMAC with SHA-256 RFC4231 MUST be supported and HMAC with SHA-1 RFC3370 SHOULD be supported.
AuthEnvelopedData
If an implementation supports AuthEnvelopedData, then it MUST implement the EnvelopedData recommendations except for the content encryption algorithm, which in this case MUST be AES-GCM RFC5084; the 128-bit version MUST be implemented and the 256-bit version SHOULD be implemented. Implementations MAY also support for AES-CCM RFC5084.
Public Key Sizes
The easiest way to implement the SignedData, EnvelopedData, and AuthEnvelopedData is with public key certificates RFC5280. If an implementation support RSA, RSASSA-PSS, DSS, RSAES-OAEP, or DH, then it MUST support key lengths from 1024-bit to 2048-bit, inclusive.
SMIMECapabilities Attribute
RFC5751 defines the SMIMECapabilities attribute as a mechanism for recipients to indicate their supported capabilities including the algorithms they support. The following are values for the SMIMECapabilities attribute for AES Key Wrap with Padding RFC5649 when used as a content encryption algorithm:
AES-128 KW with Padding: 30 0d 06 09 60 86 48 01 65 03 04 01 08 AES-192 KW with Padding: 30 0d 06 09 60 86 48 01 65 03 04 01 1C AES-256 KW with Padding: 30 0d 06 09 60 86 48 01 65 03 04 01 30
Security Considerations
The security considerations from RFC3370, RFC3560, RFC4056, RFC4231, RFC5083, RFC5084, RFC5649, RFC5652, RFC5754, and RFC5958 apply.
The strength of any encryption scheme is only as good as its weakest link, which in the case of a PBES is the password. Passwords need to provide sufficient entropy to ensure they cannot be easily guessed. The U.S. National Institute of Standards and Technology (NIST) Electronic Authentication Guidance [SP800-63] provides some information on password entropy. [SP800-63] indicates that a user- chosen 20-character password from a 94-character keyboard with no checks provides 36 bits of entropy. If the 20-character password is randomly chosen, then the amount of entropy is increased to roughly 131 bits of entropy. The amount of entropy in the password does not correlate directly to bits of security but in general the more than the better.
The choice of content encryption algorithms for this document was based on RFC5649: "In the design of some high assurance cryptographic modules, it is desirable to segregate cryptographic keying material from other data. The use of a specific cryptographic mechanism solely for the protection of cryptographic keying material can assist in this goal". Unfortunately, there is no AES-GCM or AES- CCM mode that provides the same properties. If an AES-GCM and AES- CCM mode that provides the same properties is defined, then this document will be updated to adopt that algorithm.
[SP800-57] provides comparable bits of security for some algorithms and key sizes. [SP800-57] also provides time frames during which certain numbers of bits of security are appropriate and some environments may find these time frames useful.
References
Normative References
[P12] RSA Laboratories, "PKCS #12 v1.0: Personal Information
Exchange Syntax", June 1999.
RFC2119 Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
RFC2898 Kaliski, B., "PKCS #5: Password-Based Cryptography
Specification Version 2.0", RFC 2898, September 2000.
RFC3370 Housley, R., "Cryptographic Message Syntax (CMS)
Algorithms", RFC 3370, August 2002.
RFC3560 Housley, R., "Use of the RSAES-OAEP Key Transport
Algorithm in Cryptographic Message Syntax (CMS)", RFC 3560, July 2003.
RFC4056 Schaad, J., "Use of the RSASSA-PSS Signature Algorithm in
Cryptographic Message Syntax (CMS)", RFC 4056, June 2005.
RFC4231 Nystrom, M., "Identifiers and Test Vectors for HMAC-
SHA-224, HMAC-SHA-256, HMAC-SHA-384, and HMAC-SHA-512", RFC 4231, December 2005.
RFC5083 Housley, R., "Cryptographic Message Syntax (CMS)
Authenticated-Enveloped-Data Content Type", RFC 5083, November 2007.
RFC5084 Housley, R., "Using AES-CCM and AES-GCM Authenticated
Encryption in the Cryptographic Message Syntax (CMS)", RFC 5084, November 2007.
RFC5280 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.
RFC5649 Housley, R. and M. Dworkin, "Advanced Encryption Standard
(AES) Key Wrap with Padding Algorithm", RFC 5649, September 2009.
RFC5652 Housley, R., "Cryptographic Message Syntax (CMS)", STD
70, RFC 5652, September 2009.
RFC5751 Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
Mail Extensions (S/MIME) Version 3.2 Message Specification", RFC 5751, January 2010.
RFC5754 Turner, S., "Using SHA2 Algorithms with Cryptographic
Message Syntax", RFC 5754, January 2010.
RFC5958 Turner, S., "Asymmetric Key Packages", RFC 5958, August
2010.
Informative References
[SP800-57] National Institute of Standards and Technology (NIST),
Special Publication 800-57: Recommendation for Key Management - Part 1 (Revised), March 2007.
[SP800-63] National Institute of Standards and Technology (NIST),
Special Publication 800-63: Electronic Authentication Guidance, April 2006.
Author's Address
Sean Turner IECA, Inc. 3057 Nutley Street, Suite 106 Fairfax, VA 22031 USA
EMail: [email protected]