CMSORIforPSK-2019 { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) modules(0) id-mod-cms-ori-psk-2019(69) } DEFINITIONS EXPLICIT TAGS ::= BEGIN -- EXPORTS All IMPORTS AlgorithmIdentifier{}, KEY-DERIVATION FROM AlgorithmInformation-2009 -- [RFC5912] { iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-algorithmInformation-02(58) } OTHER-RECIPIENT, OtherRecipientInfo, CMSVersion, KeyTransRecipientInfo, OriginatorIdentifierOrKey, UserKeyingMaterial, RecipientEncryptedKeys, EncryptedKey, KeyDerivationAlgorithmIdentifier, KeyEncryptionAlgorithmIdentifier FROM CryptographicMessageSyntax-2010 -- [RFC6268] { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) modules(0) id-mod-cms-2009(58) } ; -- -- OtherRecipientInfo Types (ori-) -- SupportedOtherRecipInfo OTHER-RECIPIENT ::= { ori-keyTransPSK | ori-keyAgreePSK, ... } -- -- Key Transport with Pre-Shared Key -- ori-keyTransPSK OTHER-RECIPIENT ::= { KeyTransPSKRecipientInfo IDENTIFIED BY id-ori-keyTransPSK } id-ori OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) 13 } id-ori-keyTransPSK OBJECT IDENTIFIER ::= { id-ori 1 } KeyTransPSKRecipientInfo ::= SEQUENCE { version CMSVersion, -- always set to 0 pskid PreSharedKeyIdentifier, kdfAlgorithm KeyDerivationAlgorithmIdentifier, keyEncryptionAlgorithm KeyEncryptionAlgorithmIdentifier, ktris KeyTransRecipientInfos, encryptedKey EncryptedKey } PreSharedKeyIdentifier ::= OCTET STRING KeyTransRecipientInfos ::= SEQUENCE OF KeyTransRecipientInfo -- -- Key Agreement with Pre-Shared Key -- ori-keyAgreePSK OTHER-RECIPIENT ::= { KeyAgreePSKRecipientInfo IDENTIFIED BY id-ori-keyAgreePSK } id-ori-keyAgreePSK OBJECT IDENTIFIER ::= { id-ori 2 } KeyAgreePSKRecipientInfo ::= SEQUENCE { version CMSVersion, -- always set to 0 pskid PreSharedKeyIdentifier, originator [0] EXPLICIT OriginatorIdentifierOrKey, ukm [1] EXPLICIT UserKeyingMaterial OPTIONAL, kdfAlgorithm KeyDerivationAlgorithmIdentifier, keyEncryptionAlgorithm KeyEncryptionAlgorithmIdentifier, recipientEncryptedKeys RecipientEncryptedKeys } -- -- Structure to provide 'info' input to the KDF, -- including the Pre-Shared Key -- CMSORIforPSKOtherInfo ::= SEQUENCE { psk OCTET STRING, keyMgmtAlgType ENUMERATED { keyTrans (5), keyAgree (10) }, keyEncryptionAlgorithm KeyEncryptionAlgorithmIdentifier, pskLength INTEGER (1..MAX), kdkLength INTEGER (1..MAX) } END 7. Security Considerations The security considerations related to the CMS enveloped-data content type in [RFC5652] and the security considerations related to the CMS authenticated-enveloped-data content type in [RFC5083] continue to apply. Implementations of the key derivation function must compute the entire result, which, in this specification, is a key-encryption key, before outputting any portion of the result. The resulting key- encryption key must be protected. Compromise of the key-encryption key may result in the disclosure of all content-encryption keys or content-authenticated-encryption keys that were protected with that keying material; this, in turn, may result in the disclosure of the content. Note that there are two key-encryption keys when a PSK with a key agreement algorithm is used, with similar consequences for the compromise of either one of these keys. Implementations must protect the PSK, key transport private key, agreement private key, and key-derivation key. Compromise of the PSK will make the encrypted content vulnerable to the future invention of a large-scale quantum computer. Compromise of the PSK and either the key transport private key or the agreement private key may result in the disclosure of all contents protected with that combination of keying material. Compromise of the PSK and the key-derivation key may result in the disclosure of all contents protected with that combination of keying material. A large-scale quantum computer will essentially negate the security provided by the key transport algorithm or the key agreement algorithm, which means that the attacker with a large-scale quantum computer can discover the key-derivation key. In addition, a large- scale quantum computer effectively cuts the security provided by a symmetric key algorithm in half. Therefore, the PSK needs at least 256 bits of entropy to provide 128 bits of security. To match that same level of security, the key derivation function needs to be quantum resistant and produce a key-encryption key that is at least 256 bits in length. Similarly, the content-encryption key or content-authenticated-encryption key needs to be at least 256 bits in length. When using a PSK with a key transport or a key agreement algorithm, a key-encryption key is produced to encrypt the content-encryption key or content-authenticated-encryption key. If the key-encryption algorithm is different than the algorithm used to protect the content, then the effective security is determined by the weaker of the two algorithms. If, for example, content is encrypted with 256-bit AES and the key is wrapped with 128-bit AES, then, at most, 128 bits of protection are provided. Implementers must ensure that the key-encryption algorithm is as strong or stronger than the content-encryption algorithm or content-authenticated-encryption algorithm. The selection of the key-derivation function imposes an upper bound on the strength of the resulting key-encryption key. The strength of the selected key-derivation function should be at least as strong as the key-encryption algorithm that is selected. NIST SP 800-56C Revision 1 [NIST2018] offers advice on the security strength of several popular key-derivation functions. Implementers should not mix quantum-resistant key management algorithms with their non-quantum-resistant counterparts. For example, the same content should not be protected with KeyTransRecipientInfo and KeyTransPSKRecipientInfo. Likewise, the same content should not be protected with KeyAgreeRecipientInfo and KeyAgreePSKRecipientInfo. Doing so would make the content vulnerable to the future invention of a large-scale quantum computer. Implementers should not send the same content in different messages, one using a quantum-resistant key management algorithm and the other using a non-quantum-resistant key management algorithm, even if the content-encryption key is generated independently. Doing so may allow an eavesdropper to correlate the messages, making the content vulnerable to the future invention of a large-scale quantum computer. This specification does not require that PSK be known only by the sender and recipients. The PSK may be known to a group. Since confidentiality depends on the key transport or key agreement algorithm, knowledge of the PSK by other parties does not inherently enable eavesdropping. However, group members can record the traffic of other members and then decrypt it if they ever gain access to a large-scale quantum computer. Also, when many parties know the PSK, there are many opportunities for theft of the PSK by an attacker. Once an attacker has the PSK, they can decrypt stored traffic if they ever gain access to a large-scale quantum computer in the same manner as a legitimate group member. Sound cryptographic key hygiene is to use a key for one and only one purpose. Use of the recipient's public key for both the traditional CMS and the PSK-mixing variation specified in this document would be a violation of this principle; however, there is no known way for an attacker to take advantage of this situation. That said, an application should enforce separation whenever possible. For example, a purpose identifier for use in the X.509 extended key usage certificate extension [RFC5280] could be identified in the future to indicate that a public key should only be used in conjunction with or without a PSK. Implementations must randomly generate key-derivation keys as well as content-encryption keys or content-authenticated-encryption keys. Also, the generation of public/private key pairs for the key transport and key agreement algorithms rely on random numbers. The use of inadequate pseudorandom number generators (PRNGs) to generate cryptographic keys can result in little or no security. An attacker may find it much easier to reproduce the PRNG environment that produced the keys, searching the resulting small set of possibilities, rather than brute-force searching the whole key space. The generation of quality random numbers is difficult. [RFC4086] offers important guidance in this area. Implementers should be aware that cryptographic algorithms become weaker with time. As new cryptanalysis techniques are developed and computing performance improves, the work factor to break a particular cryptographic algorithm will be reduced. Therefore, cryptographic algorithm implementations should be modular, allowing new algorithms to be readily inserted. That is, implementers should be prepared for the set of supported algorithms to change over time. The security properties provided by the mechanisms specified in this document can be validated using formal methods. A ProVerif proof in [H2019] shows that an attacker with a large-scale quantum computer that is capable of breaking the Diffie-Hellman key agreement algorithm cannot disrupt the delivery of the content-encryption key to the recipient and that the attacker cannot learn the content- encryption key from the protocol exchange. 8. Privacy Considerations An observer can see which parties are using each PSK simply by watching the PSK key identifiers. However, the addition of these key identifiers does not really weaken the privacy situation. When key transport is used, the RecipientIdentifier is always present, and it clearly identifies each recipient to an observer. When key agreement is used, either the IssuerAndSerialNumber or the RecipientKeyIdentifier is always present, and these clearly identify each recipient. 9. IANA Considerations One object identifier for the ASN.1 module in Section 6 was assigned in the "SMI Security for S/MIME Module Identifier (1.2.840.113549.1.9.16.0)" registry [IANA]: id-mod-cms-ori-psk-2019 OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) mod(0) 69 } One new entry has been added in the "SMI Security for S/MIME Mail Security (1.2.840.113549.1.9.16)" registry [IANA]: id-ori OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) 13 } A new registry titled "SMI Security for S/MIME Other Recipient Info Identifiers (1.2.840.113549.1.9.16.13)" has been created. Updates to the new registry are to be made according to the Specification Required policy as defined in [RFC8126]. The expert is expected to ensure that any new values identify additional RecipientInfo structures for use with the CMS. Object identifiers for other purposes should not be assigned in this arc. Two assignments were made in the new "SMI Security for S/MIME Other Recipient Info Identifiers (1.2.840.113549.1.9.16.13)" registry [IANA] with references to this document: id-ori-keyTransPSK OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-ori(13) 1 } id-ori-keyAgreePSK OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-ori(13) 2 } 10. References 10.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC5083] Housley, R., "Cryptographic Message Syntax (CMS) Authenticated-Enveloped-Data Content Type", RFC 5083, DOI 10.17487/RFC5083, November 2007, . [RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70, RFC 5652, DOI 10.17487/RFC5652, September 2009, . [RFC5912] Hoffman, P. and J. Schaad, "New ASN.1 Modules for the Public Key Infrastructure Using X.509 (PKIX)", RFC 5912, DOI 10.17487/RFC5912, June 2010, . [RFC6268] Schaad, J. and S. Turner, "Additional New ASN.1 Modules for the Cryptographic Message Syntax (CMS) and the Public Key Infrastructure Using X.509 (PKIX)", RFC 6268, DOI 10.17487/RFC6268, July 2011, . [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 8126, DOI 10.17487/RFC8126, June 2017, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [X680] ITU-T, "Information technology -- Abstract Syntax Notation One (ASN.1): Specification of basic notation", ITU-T Recommendation X.680, August 2015. [X690] ITU-T, "Information technology -- ASN.1 encoding rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER)", ITU-T Recommendation X.690, August 2015. 10.2. Informative References [AES] National Institute of Standards and Technology, "Advanced Encryption Standard (AES)", DOI 10.6028/NIST.FIPS.197, NIST PUB 197, November 2001, . [C2PQ] Hoffman, P., "The Transition from Classical to Post- Quantum Cryptography", Work in Progress, Internet-Draft, draft-hoffman-c2pq-06, 25 November 2019, . [FGHT2016] Fried, J., Gaudry, P., Heninger, N., and E. Thome, "A kilobit hidden SNFS discrete logarithm computation", Cryptology ePrint Archive Report 2016/961, October 2016, . [H2019] Hammell, J., "Subject: [lamps] WG Last Call for draft- ietf-lamps-cms-mix-with-psk"", message to the IETF mailing list, May 2019, . [IANA] IANA, "Structure of Management Information (SMI) Numbers (MIB Module Registrations)", . [NAS2019] National Academies of Sciences, Engineering, and Medicine, "Quantum Computing: Progress and Prospects", DOI 10.17226/25196, 2019, . [NIST2018] Barker, E., Chen, L., and R. Davis, "Recommendation for Key-Derivation Methods in Key-Establishment Schemes", NIST Special Publication 800-56C Revision 1, April 2018, . [RFC2631] Rescorla, E., "Diffie-Hellman Key Agreement Method", RFC 2631, DOI 10.17487/RFC2631, June 1999, . [RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker, "Randomness Requirements for Security", BCP 106, RFC 4086, DOI 10.17487/RFC4086, June 2005, . [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, DOI 10.17487/RFC5280, May 2008, . [RFC5753] Turner, S. and D. Brown, "Use of Elliptic Curve Cryptography (ECC) Algorithms in Cryptographic Message Syntax (CMS)", RFC 5753, DOI 10.17487/RFC5753, January 2010, . [RFC5869] Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand Key Derivation Function (HKDF)", RFC 5869, DOI 10.17487/RFC5869, May 2010, . [RFC8017] Moriarty, K., Ed., Kaliski, B., Jonsson, J., and A. Rusch, "PKCS #1: RSA Cryptography Specifications Version 2.2", RFC 8017, DOI 10.17487/RFC8017, November 2016, . [RFC8619] Housley, R., "Algorithm Identifiers for the HMAC-based Extract-and-Expand Key Derivation Function (HKDF)", RFC 8619, DOI 10.17487/RFC8619, June 2019, . [S1994] Shor, P., "Algorithms for Quantum Computation: Discrete Logarithms and Factoring", Proceedings of the 35th Annual Symposium on Foundations of Computer Science, pp. 124-134", November 1994. Appendix A. Key Transport with PSK Example This example shows the establishment of an AES-256 content-encryption key using: * a pre-shared key of 256 bits; * key transport using RSA PKCS#1 v1.5 with a 3072-bit key; * key derivation using HKDF with SHA-384; and * key wrap using AES-256-KEYWRAP. In real-world use, the originator would encrypt the key-derivation key in their own RSA public key as well as the recipient's public key. This is omitted in an attempt to simplify the example. A.1. Originator Processing Example The pre-shared key known to Alice and Bob, in hexadecimal, is: c244cdd11a0d1f39d9b61282770244fb0f6befb91ab7f96cb05213365cf95b15 The identifier assigned to the pre-shared key is: ptf-kmc:13614122112 Alice obtains Bob's public key: -----BEGIN PUBLIC KEY----- MIIBojANBgkqhkiG9w0BAQEFAAOCAY8AMIIBigKCAYEA3ocW14cxncPJ47fnEjBZ AyfC2lqapL3ET4jvV6C7gGeVrRQxWPDwl+cFYBBR2ej3j3/0ecDmu+XuVi2+s5JH Keeza+itfuhsz3yifgeEpeK8T+SusHhn20/NBLhYKbh3kiAcCgQ56dpDrDvDcLqq vS3jg/VO+OPnZbofoHOOevt8Q/roahJe1PlIyQ4udWB8zZezJ4mLLfbOA9YVaYXx 2AHHZJevo3nmRnlgJXo6mE00E/6qkhjDHKSMdl2WG6mO9TCDZc9qY3cAJDU6Ir0v SH7qUl8/vN13y4UOFkn8hM4kmZ6bJqbZt5NbjHtY4uQ0VMW3RyESzhrO02mrp39a uLNnH3EXdXaV1tk75H3qC7zJaeGWMJyQfOE3YfEGRKn8fxubji716D8UecAxAzFy FL6m1JiOyV5acAiOpxN14qRYZdHnXOM9DqGIGpoeY1UuD4Mo05osOqOUpBJHA9fS whSZG7VNf+vgNWTLNYSYLI04KiMdulnvU6ds+QPz+KKtAgMBAAE= -----END PUBLIC KEY----- Bob's RSA public key has the following key identifier: 9eeb67c9b95a74d44d2f16396680e801b5cba49c Alice randomly generates a content-encryption key: c8adc30f4a3e20ac420caa76a68f5787c02ab42afea20d19672fd963a5338e83 Alice randomly generates a key-derivation key: df85af9e3cebffde6e9b9d24263db31114d0a8e33a0d50e05eb64578ccde81eb Alice encrypts the key-derivation key in Bob's public key: 52693f12140c91dea2b44c0b7936f6be46de8a7bfab072bcb6ecfd56b06a9f65 1bd4669d336aef7b449e5cd9b151893b7c7a3b8e364394840b0a5434cbf10e1b 5670aefd074faf380665d204fb95153543346f36c2125dba6f4d23d2bc61434b 5e36ff72b3eafe57c6cf7f74924c309f174b0b8753554b58ed33a8848d707a98 c0c2b1ddcfd09e31fe213ca0a48dd157bd7d842e85cc76f77710d58efeaa0525 c651bcd1410fb47534ecabaf5ab7daabed809d4b97220caf6d4929c5fb684f7b b8692e6e70332ff9b3f7c11d6cac51d4a35593173d48f80ca843b89789d625e7 997ad7d674d25a2a7d165a5f39b3cb6358e937bdb02ac8a524ac93113cedd9ad c68263025c0bb0997d716e58d4d7b69739bf591f3e71c7678dc0df96f3df9e8a a5738f4f9ce21489f300e040891b20b2ab6d9051b3c2e68efa2fa9799a706878 d5f462018c021d6669ed649f9acdf78476810198bfb8bd41ffedc585eafa957e ea1d3625e4bed376e7ae49718aee2f575c401a26a29941d8da5b7ee9aca36471 Alice produces a 256-bit key-encryption key with HKDF using SHA-384; the secret value is the key-derivation key; and the 'info' is the DER-encoded CMSORIforPSKOtherInfo structure with the following values: 0 56: SEQUENCE { 2 32: OCTET STRING : C2 44 CD D1 1A 0D 1F 39 D9 B6 12 82 77 02 44 FB : 0F 6B EF B9 1A B7 F9 6C B0 52 13 36 5C F9 5B 15 36 1: ENUMERATED 5 39 11: SEQUENCE { 41 9: OBJECT IDENTIFIER aes256-wrap (2 16 840 1 101 3 4 1 45) : } 52 1: INTEGER 32 55 1: INTEGER 32 : } The DER encoding of CMSORIforPSKOtherInfo produces 58 octets: 30380420c244cdd11a0d1f39d9b61282770244fb0f6befb91ab7f96cb0521336 5cf95b150a0105300b060960864801650304012d020120020120 The HKDF output is 256 bits: f319e9cebb35f1c6a7a9709b8760b9d0d3e30e16c5b2b69347e9f00ca540a232 Alice uses AES-KEY-WRAP to encrypt the 256-bit content-encryption key with the key-encryption key: ea0947250fa66cd525595e52a69aaade88efcf1b0f108abe291060391b1cdf59 07f36b4067e45342 Alice encrypts the content using AES-256-GCM with the content- encryption key. The 12-octet nonce used is: cafebabefacedbaddecaf888 The content plaintext is: 48656c6c6f2c20776f726c6421 The resulting ciphertext is: 9af2d16f21547fcefed9b3ef2d The resulting 12-octet authentication tag is: a0e5925cc184e0172463c44c A.2. ContentInfo and AuthEnvelopedData Alice encodes the AuthEnvelopedData and the ContentInfo and sends the result to Bob. The resulting structure is: 0 650: SEQUENCE { 4 11: OBJECT IDENTIFIER : authEnvelopedData (1 2 840 113549 1 9 16 1 23) 17 633: [0] { 21 629: SEQUENCE { 25 1: INTEGER 0 28 551: SET { 32 547: [4] { 36 11: OBJECT IDENTIFIER : keyTransPSK (1 2 840 113549 1 9 16 13 1) 49 530: SEQUENCE { 53 1: INTEGER 0 56 19: OCTET STRING 'ptf-kmc:13614122112' 77 13: SEQUENCE { 79 11: OBJECT IDENTIFIER : hkdf-with-sha384 (1 2 840 113549 1 9 16 3 29) : } 92 11: SEQUENCE { 94 9: OBJECT IDENTIFIER : aes256-wrap (2 16 840 1 101 3 4 1 45) : } 105 432: SEQUENCE { 109 428: SEQUENCE { 113 1: INTEGER 2 116 20: [0] : 9E EB 67 C9 B9 5A 74 D4 4D 2F 16 39 66 80 E8 01 : B5 CB A4 9C 138 13: SEQUENCE { 140 9: OBJECT IDENTIFIER : rsaEncryption (1 2 840 113549 1 1 1) 151 0: NULL : } 153 384: OCTET STRING : 52 69 3F 12 14 0C 91 DE A2 B4 4C 0B 79 36 F6 BE : 46 DE 8A 7B FA B0 72 BC B6 EC FD 56 B0 6A 9F 65 : 1B D4 66 9D 33 6A EF 7B 44 9E 5C D9 B1 51 89 3B : 7C 7A 3B 8E 36 43 94 84 0B 0A 54 34 CB F1 0E 1B : 56 70 AE FD 07 4F AF 38 06 65 D2 04 FB 95 15 35 : 43 34 6F 36 C2 12 5D BA 6F 4D 23 D2 BC 61 43 4B : 5E 36 FF 72 B3 EA FE 57 C6 CF 7F 74 92 4C 30 9F : 17 4B 0B 87 53 55 4B 58 ED 33 A8 84 8D 70 7A 98 : C0 C2 B1 DD CF D0 9E 31 FE 21 3C A0 A4 8D D1 57 : BD 7D 84 2E 85 CC 76 F7 77 10 D5 8E FE AA 05 25 : C6 51 BC D1 41 0F B4 75 34 EC AB AF 5A B7 DA AB : ED 80 9D 4B 97 22 0C AF 6D 49 29 C5 FB 68 4F 7B : B8 69 2E 6E 70 33 2F F9 B3 F7 C1 1D 6C AC 51 D4 : A3 55 93 17 3D 48 F8 0C A8 43 B8 97 89 D6 25 E7 : 99 7A D7 D6 74 D2 5A 2A 7D 16 5A 5F 39 B3 CB 63 : 58 E9 37 BD B0 2A C8 A5 24 AC 93 11 3C ED D9 AD : C6 82 63 02 5C 0B B0 99 7D 71 6E 58 D4 D7 B6 97 : 39 BF 59 1F 3E 71 C7 67 8D C0 DF 96 F3 DF 9E 8A : A5 73 8F 4F 9C E2 14 89 F3 00 E0 40 89 1B 20 B2 : AB 6D 90 51 B3 C2 E6 8E FA 2F A9 79 9A 70 68 78 : D5 F4 62 01 8C 02 1D 66 69 ED 64 9F 9A CD F7 84 : 76 81 01 98 BF B8 BD 41 FF ED C5 85 EA FA 95 7E : EA 1D 36 25 E4 BE D3 76 E7 AE 49 71 8A EE 2F 57 : 5C 40 1A 26 A2 99 41 D8 DA 5B 7E E9 AC A3 64 71 : } : } 541 40: OCTET STRING : EA 09 47 25 0F A6 6C D5 25 59 5E 52 A6 9A AA DE : 88 EF CF 1B 0F 10 8A BE 29 10 60 39 1B 1C DF 59 : 07 F3 6B 40 67 E4 53 42 : } : } : } 583 55: SEQUENCE { 585 9: OBJECT IDENTIFIER data (1 2 840 113549 1 7 1) 596 27: SEQUENCE { 598 9: OBJECT IDENTIFIER : aes256-GCM (2 16 840 1 101 3 4 1 46) 609 14: SEQUENCE { 611 12: OCTET STRING : CA FE BA BE FA CE DB AD DE CA F8 88 : } : } 625 13: [0] : 9A F2 D1 6F 21 54 7F CE FE D9 B3 EF 2D : } 640 12: OCTET STRING A0 E5 92 5C C1 84 E0 17 24 63 C4 4C : } : } : } A.3. Recipient Processing Example Bob's private key is: -----BEGIN RSA PRIVATE KEY----- MIIG5AIBAAKCAYEA3ocW14cxncPJ47fnEjBZAyfC2lqapL3ET4jvV6C7gGeVrRQx WPDwl+cFYBBR2ej3j3/0ecDmu+XuVi2+s5JHKeeza+itfuhsz3yifgeEpeK8T+Su sHhn20/NBLhYKbh3kiAcCgQ56dpDrDvDcLqqvS3jg/VO+OPnZbofoHOOevt8Q/ro ahJe1PlIyQ4udWB8zZezJ4mLLfbOA9YVaYXx2AHHZJevo3nmRnlgJXo6mE00E/6q khjDHKSMdl2WG6mO9TCDZc9qY3cAJDU6Ir0vSH7qUl8/vN13y4UOFkn8hM4kmZ6b JqbZt5NbjHtY4uQ0VMW3RyESzhrO02mrp39auLNnH3EXdXaV1tk75H3qC7zJaeGW MJyQfOE3YfEGRKn8fxubji716D8UecAxAzFyFL6m1JiOyV5acAiOpxN14qRYZdHn XOM9DqGIGpoeY1UuD4Mo05osOqOUpBJHA9fSwhSZG7VNf+vgNWTLNYSYLI04KiMd ulnvU6ds+QPz+KKtAgMBAAECggGATFfkSkUjjJCjLvDk4aScpSx6+Rakf2hrdS3x jwqhyUfAXgTTeUQQBs1HVtHCgxQd+qlXYn3/qu8TeZVwG4NPztyi/Z5yB1wOGJEV 3k8N/ytul6pJFFn6p48VM01bUdTrkMJbXERe6g/rr6dBQeeItCaOK7N5SIJH3Oqh 9xYuB5tH4rquCdYLmt17Tx8CaVqU9qPY3vOdQEOwIjjMV8uQUR8rHSO9KkSj8AGs Lq9kcuPpvgJc2oqMRcNePS2WVh8xPFktRLLRazgLP8STHAtjT6SlJ2UzkUqfDHGK q/BoXxBDu6L1VDwdnIS5HXtL54ElcXWsoOyKF8/ilmhRUIUWRZFmlS1ok8IC5IgX UdL9rJVZFTRLyAwmcCEvRM1asbBrhyEyshSOuN5nHJi2WVJ+wSHijeKl1qeLlpMk HrdIYBq4Nz7/zXmiQphpAy+yQeanhP8O4O6C8e7RwKdpxe44su4Z8fEgA5yQx0u7 8yR1EhGKydX5bhBLR5Cm1VM7rT2BAoHBAP/+e5gZLNf/ECtEBZjeiJ0VshszOoUq haUQPA+9Bx9pytsoKm5oQhB7QDaxAvrn8/FUW2aAkaXsaj9F+/q30AYSQtExai9J fdKKook3oimN8/yNRsKmhfjGOj8hd4+GjX0qoMSBCEVdT+bAjjry8wgQrqReuZnu oXU85dmb3jvv0uIczIKvTIeyjXE5afjQIJLmZFXsBm09BG87Ia5EFUKly96BOMJh /QWEzuYYXDqOFfzQtkAefXNFW21Kz4Hw2QKBwQDeiGh4lxCGTjECvG7fauMGlu+q DSdYyMHif6t6mx57eS16EjvOrlXKItYhIyzW8Kw0rf/CSB2j8ig1GkMLTOgrGIJ1 0322o50FOr5oOmZPueeR4pOyAP0fgQ8DD1L3JBpY68/8MhYbsizVrR+Ar4jM0f96 W2bF5Xj3h+fQTDMkx6VrCCQ6miRmBUzH+ZPs5n/lYOzAYrqiKOanaiHy4mjRvlsy mjZ6z5CG8sISqcLQ/k3Qli5pOY/v0rdBjgwAW/UCgcEAqGVYGjKdXCzuDvf9EpV4 mpTWB6yIV2ckaPOn/tZi5BgsmEPwvZYZt0vMbu28Px7sSpkqUuBKbzJ4pcy8uC3I SuYiTAhMiHS4rxIBX3BYXSuDD2RD4vG1+XM0h6jVRHXHh0nOXdVfgnmigPGz3jVJ B8oph/jD8O2YCk4YCTDOXPEi8Rjusxzro+whvRR+kG0gsGGcKSVNCPj1fNISEte4 gJId7O1mUAAzeDjn/VaS/PXQovEMolssPPKn9NocbKbpAoHBAJnFHJunl22W/lrr ppmPnIzjI30YVcYOA5vlqLKyGaAsnfYqP1WUNgfVhq2jRsrHx9cnHQI9Hu442PvI x+c5H30YFJ4ipE3eRRRmAUi4ghY5WgD+1hw8fqyUW7E7l5LbSbGEUVXtrkU5G64T UR91LEyMF8OPATdiV/KD4PWYkgaqRm3tVEuCVACDTQkqNsOOi3YPQcm270w6gxfQ SOEy/kdhCFexJFA8uZvmh6Cp2crczxyBilR/yCxqKOONqlFdOQKBwFbJk5eHPjJz AYueKMQESPGYCrwIqxgZGCxaqeVArHvKsEDx5whI6JWoFYVkFA8F0MyhukoEb/2x 2qB5T88Dg3EbqjTiLg3qxrWJ2OxtUo8pBP2I2wbl2NOwzcbrlYhzEZ8bJyxZu5i1 sYILC8PJ4Qzw6jS4Qpm4y1WHz8e/ElW6VyfmljZYA7f9WMntdfeQVqCVzNTvKn6f hg6GSpJTzp4LV3ougi9nQuWXZF2wInsXkLYpsiMbL6Fz34RwohJtYA== -----END RSA PRIVATE KEY----- Bob decrypts the key-derivation key with his RSA private key: df85af9e3cebffde6e9b9d24263db31114d0a8e33a0d50e05eb64578ccde81eb Bob produces a 256-bit key-encryption key with HKDF using SHA-384; the secret value is the key-derivation key; and the 'info' is the DER-encoded CMSORIforPSKOtherInfo structure with the same values as shown in Appendix A.1. The HKDF output is 256 bits: f319e9cebb35f1c6a7a9709b8760b9d0d3e30e16c5b2b69347e9f00ca540a232 Bob uses AES-KEY-WRAP to decrypt the content-encryption key with the key-encryption key; the content-encryption key is: c8adc30f4a3e20ac420caa76a68f5787c02ab42afea20d19672fd963a5338e83 Bob decrypts the content using AES-256-GCM with the content- encryption key and checks the received authentication tag. The 12-octet nonce used is: cafebabefacedbaddecaf888 The 12-octet authentication tag is: a0e5925cc184e0172463c44c The received ciphertext content is: 9af2d16f21547fcefed9b3ef2d The resulting plaintext content is: 48656c6c6f2c20776f726c6421 Appendix B. Key Agreement with PSK Example This example shows the establishment of an AES-256 content-encryption key using: * a pre-shared key of 256 bits; * key agreement using ECDH on curve P-384 and X9.63 KDF with SHA- 384; * key derivation using HKDF with SHA-384; and * key wrap using AES-256-KEYWRAP. In real-world use, the originator would treat themselves as an additional recipient by performing key agreement with their own static public key and the ephemeral private key generated for this message. This is omitted in an attempt to simplify the example. B.1. Originator Processing Example The pre-shared key known to Alice and Bob, in hexadecimal, is: 4aa53cbf500850dd583a5d9821605c6fa228fb5917f87c1c078660214e2d83e4 The identifier assigned to the pre-shared key is: ptf-kmc:216840110121 Alice randomly generates a content-encryption key: 937b1219a64d57ad81c05cc86075e86017848c824d4e85800c731c5b7b091033 Alice obtains Bob's static ECDH public key: -----BEGIN PUBLIC KEY----- MHYwEAYHKoZIzj0CAQYFK4EEACIDYgAEScGPBO9nmUwGrgbGEoFY9HR/bCo0WyeY /dePQVrwZmwN2yMJmO2d1kWCvLTz8U7atinxyIRe9CV54yau1KWU/wbkhPDnzuSM YkcpxMGo32z3JetEloW5aFOja13vv/W5 -----END PUBLIC KEY----- It has a key identifier of: e8218b98b8b7d86b5e9ebdc8aeb8c4ecdc05c529 Alice generates an ephemeral ECDH key pair on the same curve: -----BEGIN EC PRIVATE KEY----- MIGkAgEBBDCMiWLG44ik+L8cYVvJrQdLcFA+PwlgRF+Wt1Ab25qUh8OB7OePWjxp /b8P6IOuI6GgBwYFK4EEACKhZANiAAQ5G0EmJk/2ks8sXY1kzbuG3Uu3ttWwQRXA LFDJICjvYfr+yTpOQVkchm88FAh9MEkw4NKctokKNgpsqXyrT3DtOg76oIYENpPb GE5lJdjPx9sBsZQdABwlsU0Zb7P/7i8= -----END EC PRIVATE KEY----- Alice computes a shared secret called "Z" using Bob's static ECDH public key and her ephemeral ECDH private key; Z is: 3f015ed0ff4b99523a95157bbe77e9cc0ee52fcffeb7e41eac79d1c11b6cc556 19cf8807e6d800c2de40240fe0e26adc Alice computes the pairwise key-encryption key, called "KEK1", from Z using the X9.63 KDF with the ECC-CMS-SharedInfo structure with the following values: 0 21: SEQUENCE { 2 11: SEQUENCE { 4 9: OBJECT IDENTIFIER aes256-wrap (2 16 840 1 101 3 4 1 45) : } 15 6: [2] { 17 4: OCTET STRING 00 00 00 20 : } : } The DER encoding of ECC-CMS-SharedInfo produces 23 octets: 3015300b060960864801650304012da206040400000020 The X9.63 KDF output is the 256-bit KEK1: 27dc25ddb0b425f7a968ceada80a8f73c6ccaab115baafcce4a22a45d6b8f3da Alice produces the 256-bit KEK2 with HKDF using SHA-384; the secret value is KEK1; and the 'info' is the DER-encoded CMSORIforPSKOtherInfo structure with the following values: 0 56: SEQUENCE { 2 32: OCTET STRING : 4A A5 3C BF 50 08 50 DD 58 3A 5D 98 21 60 5C 6F : A2 28 FB 59 17 F8 7C 1C 07 86 60 21 4E 2D 83 E4 36 1: ENUMERATED 10 39 11: SEQUENCE { 41 9: OBJECT IDENTIFIER aes256-wrap (2 16 840 1 101 3 4 1 45) : } 52 1: INTEGER 32 55 1: INTEGER 32 : } The DER encoding of CMSORIforPSKOtherInfo produces 58 octets: 303804204aa53cbf500850dd583a5d9821605c6fa228fb5917f87c1c07866021 4e2d83e40a010a300b060960864801650304012d020120020120 The HKDF output is the 256-bit KEK2: 7de693ee30ae22b5f8f6cd026c2164103f4e1430f1ab135dc1fb98954f9830bb Alice uses AES-KEY-WRAP to encrypt the content-encryption key with the KEK2; the wrapped key is: 229fe0b45e40003e7d8244ec1b7e7ffb2c8dca16c36f5737222553a71263a92b de08866a602d63f4 Alice encrypts the content using AES-256-GCM with the content- encryption key. The 12-octet nonce used is: dbaddecaf888cafebabeface The plaintext is: 48656c6c6f2c20776f726c6421 The resulting ciphertext is: fc6d6f823e3ed2d209d0c6ffcf The resulting 12-octet authentication tag is: 550260c42e5b29719426c1ff B.2. ContentInfo and AuthEnvelopedData Alice encodes the AuthEnvelopedData and the ContentInfo and sends the result to Bob. The resulting structure is: 0 327: SEQUENCE { 4 11: OBJECT IDENTIFIER : authEnvelopedData (1 2 840 113549 1 9 16 1 23) 17 310: [0] { 21 306: SEQUENCE { 25 1: INTEGER 0 28 229: SET { 31 226: [4] { 34 11: OBJECT IDENTIFIER : keyAgreePSK (1 2 840 113549 1 9 16 13 2) 47 210: SEQUENCE { 50 1: INTEGER 0 53 20: OCTET STRING 'ptf-kmc:216840110121' 75 85: [0] { 77 83: [1] { 79 19: SEQUENCE { 81 6: OBJECT IDENTIFIER : ecdhX963KDF-SHA256 (1 3 132 1 11 1) 89 9: OBJECT IDENTIFIER : aes256-wrap (2 16 840 1 101 3 4 1 45) : } 100 60: BIT STRING, encapsulates { 103 57: OCTET STRING : 1B 41 26 26 4F F6 92 CF 2C 5D 8D 64 CD BB 86 DD : 4B B7 B6 D5 B0 41 15 C0 2C 50 C9 20 28 EF 61 FA : FE C9 3A 4E 41 59 1C 86 6F 3C 14 08 7D 30 49 30 : E0 D2 9C B6 89 0A 36 0A 6C : } : } : } 162 13: SEQUENCE { 164 11: OBJECT IDENTIFIER : hkdf-with-sha384 (1 2 840 113549 1 9 16 3 29) : } 177 11: SEQUENCE { 179 9: OBJECT IDENTIFIER : aes256-wrap (2 16 840 1 101 3 4 1 45) : } 190 68: SEQUENCE { 192 66: SEQUENCE { 194 22: [0] { 196 20: OCTET STRING : E8 21 8B 98 B8 B7 D8 6B 5E 9E BD C8 AE B8 C4 EC : DC 05 C5 29 : } 218 40: OCTET STRING : 22 9F E0 B4 5E 40 00 3E 7D 82 44 EC 1B 7E 7F FB : 2C 8D CA 16 C3 6F 57 37 22 25 53 A7 12 63 A9 2B : DE 08 86 6A 60 2D 63 F4 : } : } : } : } : } 260 55: SEQUENCE { 262 9: OBJECT IDENTIFIER data (1 2 840 113549 1 7 1) 273 27: SEQUENCE { 275 9: OBJECT IDENTIFIER : aes256-GCM (2 16 840 1 101 3 4 1 46) 286 14: SEQUENCE { 288 12: OCTET STRING : DB AD DE CA F8 88 CA FE BA BE FA CE : } : } 302 13: [0] : FC 6D 6F 82 3E 3E D2 D2 09 D0 C6 FF CF : } 317 12: OCTET STRING 55 02 60 C4 2E 5B 29 71 94 26 C1 FF : } : } : } B.3. Recipient Processing Example Bob obtains Alice's ephemeral ECDH public key from the message: -----BEGIN PUBLIC KEY----- MHYwEAYHKoZIzj0CAQYFK4EEACIDYgAEORtBJiZP9pLPLF2NZM27ht1Lt7bVsEEV wCxQySAo72H6/sk6TkFZHIZvPBQIfTBJMODSnLaJCjYKbKl8q09w7ToO+qCGBDaT 2xhOZSXYz8fbAbGUHQAcJbFNGW+z/+4v -----END PUBLIC KEY----- Bob's static ECDH private key is: -----BEGIN EC PRIVATE KEY----- MIGkAgEBBDAnJ4hB+tTUN9X03/W0RsrYy+qcptlRSYkhaDIsQYPXfTU0ugjJEmRk NTPj4y1IRjegBwYFK4EEACKhZANiAARJwY8E72eZTAauBsYSgVj0dH9sKjRbJ5j9 149BWvBmbA3bIwmY7Z3WRYK8tPPxTtq2KfHIhF70JXnjJq7UpZT/BuSE8OfO5Ixi RynEwajfbPcl60SWhbloU6NrXe+/9bk= -----END EC PRIVATE KEY----- Bob computes a shared secret called "Z" using Alice's ephemeral ECDH public key and his static ECDH private key; Z is: 3f015ed0ff4b99523a95157bbe77e9cc0ee52fcffeb7e41eac79d1c11b6cc556 19cf8807e6d800c2de40240fe0e26adc Bob computes the pairwise key-encryption key, KEK1, from Z using the X9.63 KDF with the ECC-CMS-SharedInfo structure with the values shown in Appendix B.1. The X9.63 KDF output is the 256-bit KEK1: 27dc25ddb0b425f7a968ceada80a8f73c6ccaab115baafcce4a22a45d6b8f3da Bob produces the 256-bit KEK2 with HKDF using SHA-384; the secret value is KEK1; and the 'info' is the DER-encoded CMSORIforPSKOtherInfo structure with the values shown in Appendix B.1. The HKDF output is the 256-bit KEK2: 7de693ee30ae22b5f8f6cd026c2164103f4e1430f1ab135dc1fb98954f9830bb Bob uses AES-KEY-WRAP to decrypt the content-encryption key with the KEK2; the content-encryption key is: 937b1219a64d57ad81c05cc86075e86017848c824d4e85800c731c5b7b091033 Bob decrypts the content using AES-256-GCM with the content- encryption key and checks the received authentication tag. The 12-octet nonce used is: dbaddecaf888cafebabeface The 12-octet authentication tag is: 550260c42e5b29719426c1ff The received ciphertext content is: fc6d6f823e3ed2d209d0c6ffcf The resulting plaintext content is: 48656c6c6f2c20776f726c6421 Acknowledgements Many thanks to Roman Danyliw, Ben Kaduk, Burt Kaliski, Panos Kampanakis, Jim Schaad, Robert Sparks, Sean Turner, and Daniel Van Geest for their review and insightful comments. They have greatly improved the design, clarity, and implementation guidance. Author's Address Russ Housley Vigil Security, LLC 516 Dranesville Road Herndon, VA 20170 United States of America Email: housley@vigilsec.com
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