Using PKCS #7 (Crypto Message Syntax)

[richardschneider]

PKCS 7: Cryptographic Message Syntax aka RFC 2315 RFC 5652 could be used to protect data. Basically PBNode.Data becomes an ASN.1 type ContentInfo

Pros

• well accepted standard that meets many needs
• could reduce PBNode.PBEncrypted to a simple Boolean
• The DAG PBNode.Data then becomes self describing CMS message
• Signing and pre-authorised people come for free

Cons

• I hate ASN.1 and OIDs more than ProtoBuf
• It requires IPFS to use X.509 certificates X.500 Distinguished Names

[richardschneider]

How do we map PBEncrypted into PKCS 7?

It looks like Enveloped-data content type should be used if the KeyHolder is not specified.

• KeyID the multihash of the key used to encrypt DataKey
  is mapped to RecipientInfo.issuerAndSerialNumber
• DataKey an ephemeral symmetric key used to decrypt the Data. Its encrypted with the KeyId
  is mapped to RecipientInfo.encryptedKey
• KeyMethod asymmetric encryption method used on DataKey, such as rsa-*
  is mapped to RecipientInfo.keyEncryptionAlgorithm
• DataMethod symmetric encryption method used on Data, such as aes-*
  is mapped to EncryptedContentInfo.contentEncryptionAlgorithm

See https://tools.ietf.org/html/rfc3370 for algorithm IDs

[richardschneider]

It looks like Cryptographic Message Syntax can be used for IPFS Encrypted data.

openssl cms -in foo.p7 -noout -cmsout -print -inform DER

CMS_ContentInfo:
  contentType: pkcs7-envelopedData (1.2.840.113549.1.7.3)
  d.envelopedData:
    version: <ABSENT>
    originatorInfo: <ABSENT>
    recipientInfos:
      d.ktri:
        version: <ABSENT>
        d.issuerAndSerialNumber:
          issuer: O=ipfs, OU=keystore, CN=QmWc1hrWTsh1sWkCKn5hd5AvMD4ZhRFwEtok2MhCAzpuvx
          serialNumber: 1
        keyEncryptionAlgorithm:
          algorithm: rsaEncryption (1.2.840.113549.1.1.1)
          parameter: NULL
        encryptedKey:
          0000 - 7e 91 56 8c d7 27 c8 42-7e d8 76 cc c2 c6 32   ~.V..'.B~.v...2
          000f - e2 7a fc 3f 6b 3e 13 9f-db 6f b9 26 5b ac b8   .z.?k>...o.&[..
          001e - 53 04 1d fa 5a 4e 02 dc-fc 2d ca 5c 60 6d 91   S...ZN...-.\`m.
          002d - f0 66 12 73 06 18 5a 08-30 e0 48 86 d2 5f b9   .f.s..Z.0.H.._.
          003c - a0 37 40 18 f6 f3 92 f5-91 32 8c f8 a5 83 64   .7@......2....d
          004b - f0 6d c0 25 0a a3 7e 3d-7d 4a 0b 0e ea 0d a1   .m.%..~=}J.....
          005a - ae 01 5b fb 60 05 19 ca-60 36 62 e7 0d b1 16   ..[.`...`6b....
          0069 - d2 b5 03 26 b8 c7 ca ee-f5 b8 e6 b0 01 c2 2f   ...&........../
          0078 - 3e 35 72 30 53 e9 3a 53-d3 89 5e 2a c0 5d 2a   >5r0S.:S..^*.]*
          0087 - cd 9b 81 c1 6e c2 ed 45-68 86 e6 1f 3a 26 62   ....n..Eh...:&b
          0096 - e3 54 5c 53 29 86 a9 ed-0d 6d 7b 38 6a 67 ab   .T\S)....m{8jg.
          00a5 - 7a 6a 19 49 d1 0a 2b a6-6e f6 d5 30 03 7c a3   zj.I..+.n..0.|.
          00b4 - 88 fe c0 a2 ec ba f7 b0-39 2c 55 15 9e eb 26   ........9,U...&
          00c3 - 9b 11 30 4b b5 5a d7 b9-0a 70 b4 24 70 90 0a   ..0K.Z...p.$p..
          00d2 - 04 62 65 8d 3b 43 4b 8a-4f e4 5a cc f7 42 68   .be.;CK.O.Z..Bh
          00e1 - 30 46 7b 9c 05 96 d2 47-0d fb 44 24 0e c9 cd   0F{....G..D$...
          00f0 - 1a 3e 5a 64 49 ce 38 e1-a6 89 01 69 7c 60 60   .>ZdI.8....i|``
          00ff - 51                                             Q
    encryptedContentInfo:
      contentType: pkcs7-data (1.2.840.113549.1.7.1)
      contentEncryptionAlgorithm:
        algorithm: aes-256-cbc (2.16.840.1.101.3.4.1.42)
        parameter: OCTET STRING:
          0000 - ad db e3 ed 6b be 3c d1-0c 44 84 4a 09 9c 02   ....k.<..D.J...
          000f - 17                                             .
      encryptedContent:
        0000 - c5 89 41 f5 12 69 6e 94-07 aa 8e 6e f3 cc 7b   ..A..in....n..{
        000f - 17 51 96 50 fc a4 e2 80-24 b5 d4 77 24 22 b7   .Q.P....$..w$".
        001e - c4 49 fe 30 08 30 bb d8-0e ed 69 60 0d bc a0   .I.0.0....i`...
        002d - 8c 03 c5                                       ...
    unprotectedAttrs:
      <EMPTY>

[richardschneider]

Note that the issuer common name (CN=QmWc1hrWTsh1sWkCKn5hd5AvMD4ZhRFwEtok2MhCAzpuvx) is the key.id from the keystore. This allows the reader to easily decrypt if the key is present in the keystore.