[lamps] EST CSR attrs discussion

[Dan Harkins <[e-mail]>]

   Hi,

   Sorry, I wasn't aware that this issue was being discussed and I wasn't
on the lamps/spasm list. But I'm largely responsible-- i.e. to blame-- for
the CSR Attrs text in RFC 7030 so perhaps I can try and explain.

   The intent of the CSR Attrs request is for the RA to ask the client
to construct the CSR in some particular way, not to impose values on
particular fields.

   As a for-instance, the RA could ask the client to:

    1. generate a public key in the NIST p384 curve;
    2. use ECDSA w/SHA384 to sign
    3. include the challengePassword
    4. include an extension with the device's serial number, a subject alt
       name, and its favorite drink

by sending the following base64-encoded blob:

ME4GCSqGSIb3DQEJBzASBgcqhkjOPQIBMQcGBSuBBAAiMCMGCSqGSIb3DQEJDjEWBgNVBAUGA1UdEQYKCZImiZPyLGQBBQYIKoZIzj0EAwM

That gets ASN.1 decoded as:

SEQUENCE (4 elem)
   OBJECT IDENTIFIER 1.2.840.113549.1.9.7 challengePassword (PKCS #9)
   SEQUENCE (2 elem)
     OBJECT IDENTIFIER 1.2.840.10045.2.1 ecPublicKey (ANSI X9.62 public 
key type)
     SET (1 elem)
       OBJECT IDENTIFIER 1.3.132.0.34 secp384r1 (SECG (Certicom) named 
elliptic curve)
   SEQUENCE (2 elem)
     OBJECT IDENTIFIER 1.2.840.113549.1.9.14 extensionRequest (PKCS #9 
via CRMF)
     SET (3 elem)
       OBJECT IDENTIFIER 2.5.4.5 serialNumber (X.520 DN component)
       OBJECT IDENTIFIER 2.5.29.17 subjectAltName (X.509 extension)
       OBJECT IDENTIFIER 0.9.2342.19200300.100.1.5 (favorite drink)
   OBJECT IDENTIFIER 1.2.840.10045.4.3.3 ecdsaWithSHA384 (ANSI X9.62 
ECDSA algorithm with SHA384)

And the client produces a CSR with an extension that gives its serial 
number,
some alternative name, and whatever drink it prefers. The idea isn't 
that the
RA would say, "your serial number is 279372 and you like scotch", it's "what
is your serial number and favorite drink?".

   If the RA wanted a particular length of RSA key, let's say of 3072 
bits, to
sign with a hash function appropriate for that bit length, and include the
challengePassword it would ask thusly:

MCkGCSqGSIb3DQEJBzARBgkqhkiG9w0BAQExBAICDAAGCSqGSIb3DQEBCw==

which gets decoded as:

SEQUENCE (3 elem)
   OBJECT IDENTIFIER 1.2.840.113549.1.9.7 challengePassword (PKCS #9)
   SEQUENCE (2 elem)
     OBJECT IDENTIFIER 1.2.840.113549.1.1.1 rsaEncryption (PKCS #1)
     SET (1 elem)
       INTEGER 3072
   OBJECT IDENTIFIER 1.2.840.113549.1.1.11 sha256WithRSAEncryption (PKCS #1)

   The idea is, this is a request to the client on how to generate a CSR in
the form that the CA expects/wants. One asks what a subject alternative name
would be, it doesn't impose one on the client.

   That was the intent anyway. And that's how I implemented it in my EST
reference implementation.

   regards,

   Dan.

-- 
"The object of life is not to be on the side of the majority, but to
escape finding oneself in the ranks of the insane." -- Marcus Aurelius