Encode DER attestation

[SmartLayer]

Let's simplify the attestation format here: https://community.tokenscript.org/t/weekly-design-meeting-16-simple-attestation-format/302

Into:

ISSUE15 DEFINITIONS ::= BEGIN
  Attestation ::=  SEQUENCE  {
       signedInfo           SignedInfo,
       signatureAlgorithm   AlgorithmIdentifier,
       signatureValue       BIT STRING  }

  SignedInfo  ::=  SEQUENCE  {
       version         [0]  EXPLICIT Version,
       serialNumber         CertificateSerialNumber,
       signature            AlgorithmIdentifier,
       dataObject   [3]      TicketDataObject
  }

  TicketDataObject ::= SEQUENCE {
         match       INTEGER (1..51),
         class       ENUMERATED { club(0), lounge(1), silver(2), gold(3) },
         admission   INTEGER
  }

  Version  ::=  INTEGER  {  v1(0), v2(1), v3(2)  }

  CertificateSerialNumber  ::=  INTEGER

  AlgorithmIdentifier  ::=  SEQUENCE  {
        algorithm               OBJECT IDENTIFIER,
        parameters              ANY DEFINED BY algorithm OPTIONAL }

END

I manually (spent 2 hours) produced an attestation with the right format (but wrong value - the signature is wrong, I made it up). I first found some ecdsa X.509 files from my computer using this command:

$ for i in /usr/share/ca-certificates/mozilla/*.crt; do echo $i; openssl asn1parse -in "$i" 2>/dev/null | grep ecdsa.*256 ; done;

Then modified an existing attestation into what I want. This is it:

$ xxd -p < /tmp/new_cert.crt
30819e3026a00302010202082c299c5b16ed0595300a06082a8648ce3d04
030230090201010a0101020101300a06082a8648ce3d0403020368003065
0231008ae6408937ebe9d513d9cad46b24f3b03d8746581aecb1df6ffb56
ba706bc738cce8b18c4f0ff7f167760e83d01e518f02303df62328264cc6
608793269bb2351ebad6f73cd11ccefa253ca61a81155bf3120f6cee658a
c987a8f907e0629a8c5c4a

Which gives:

$ openssl asn1parse -inform DER -in /tmp/new_cert.crt 
    0:d=0  hl=3 l= 158 cons: SEQUENCE          
    3:d=1  hl=2 l=  38 cons: SEQUENCE          
    5:d=2  hl=2 l=   3 cons: cont [ 0 ]        
    7:d=3  hl=2 l=   1 prim: INTEGER           :02
   10:d=2  hl=2 l=   8 prim: INTEGER           :2C299C5B16ED0595
   20:d=2  hl=2 l=  10 cons: SEQUENCE          
   22:d=3  hl=2 l=   8 prim: OBJECT            :ecdsa-with-SHA256
   32:d=2  hl=2 l=   9 cons: SEQUENCE          
   34:d=3  hl=2 l=   1 prim: INTEGER           :01
   37:d=3  hl=2 l=   1 prim: ENUMERATED        :01
   40:d=3  hl=2 l=   1 prim: INTEGER           :01
   43:d=1  hl=2 l=  10 cons: SEQUENCE          
   45:d=2  hl=2 l=   8 prim: OBJECT            :ecdsa-with-SHA256
   55:d=1  hl=2 l= 104 prim: BIT STRING        

encoded to base64:

$ base64 < /tmp/new_cert.crt | tr '/+' '_-' 
MIGeMCagAwIBAgIILCmcWxbtBZUwCgYIKoZIzj0EAwIwCQIBAQoBAQIBATAKBggqhkjOPQQDAgNo
ADBlAjEAiuZAiTfr6dUT2crUayTzsD2HRlga7LHfb_tWunBrxzjM6LGMTw_38Wd2DoPQHlGPAjA9
9iMoJkzGYIeTJpuyNR661vc80RzO-iU8phqBFVvzEg9s7mWKyYeo-QfgYpqMXEo=