Connector Identifiers (Connector IDs)

Each connector in the IDS needs a valid, outlasting and unique identifier, never be re-used for any other resource inside the IDS ecosystem.

The architecture aims to be open to multiple Certificate Authorities (CAs) issuing certificates. This means, a truly unique identifier needs to consist of the issuer of the certificate and the subject identifier. For an easy machine readable identifier, two ´X.509v3´ extensions will be used:

Subject Key Identifier (SKI)
Authority Key Identifier (AKI)

The AKI MUST include a key identifier according to RFC 5280. Key identifiers MUST be obtained as the 160-bit SHA-1 hash of the value of the BIT STRING subjectPuclicKey (excluding the tag, length, and number of unused bits) for the SKI and as a similar hash of the issuing public key for the AKI. The concatenation of ´SKI´ and ´AKI´ according to the encoding below provides a unique identifier - even if multiple CAs are able to issue valid certificates. We note that the construction presented below corresponds to the textual representation for certificates used by OpenSSL.

Construction

Let ski be the binary representation of the "raw" SKI (i.e. the 160 Hash bits), aki the binary representation of the "raw" AKI, '|' denote string concatenation, a[n] denote n-th byte (zero-indexed) of a in Network Byte Order, and Hex(x) the hexadecimal representation of the byte x using capital letters.

The connector ID is

connector_id := skiHex | ':keyid:' | akiHex

where

skiHex := Hex(ski[0]) | ':' | Hex(ski[1]) | ':' | [omitted for brievity] | ':' | Hex(ski[19])

akiHex := Hex(aki[0]) | ':' | Hex(aki[1]) | ':' | [omitted for brievity] | ':' | Hex(aki[19])

Examples

Raw construction

Let the Subject Key Identifier (in Hex notation) be

DDCBFD0B9384330111EB5D949488BE787D57FC4A

and the Key Identifier of the Authority Key Identifier be

CB8CC7B68579A823A6CB15AB17502FE665435DE8

Then

skiHex = DD:CB:FD:0B:93:84:33:01:11:EB:5D:94:94:88:BE:78:7D:57:FC:4A
akiHex = CB:8C:C7:B6:85:79:A8:23:A6:CB:15:AB:17:50:2F:E6:65:43:5D:E8
connector_id = DD:CB:FD:0B:93:84:33:01:11:EB:5D:94:94:88:BE:78:7D:57:FC:4A:keyid:CB:8C:C7:B6:85:79:A8:23:A6:CB:15:AB:17:50:2F:E6:65:43:5D:E8

Simplified Construction using the OpenSSL CLI

The following is a snippet from a X.509 certificate in text format obtained via openssl x509 -in your_certificate -noout -text:

...
X509v3 extensions:
    X509v3 Subject Key Identifier:
        DD:CB:FD:0B:93:84:33:01:11:EB:5D:94:94:88:BE:78:7D:57:FC:4A
    X509v3 Authority Key Identifier:
        keyid:CB:8C:C7:B6:85:79:A8:23:A6:CB:15:AB:17:50:2F:E6:65:43:5D:E8
...

Concatenating the values with ':' leads to the unique connector identifier:

DD:CB:FD:0B:93:84:33:01:11:EB:5D:94:94:88:BE:78:7D:57:FC:4A:keyid:CB:8C:C7:B6:85:79:A8:23:A6:CB:15:AB:17:50:2F:E6:65:43:5D:E8

Notes

In examples and for reasons of readability editors might use

SKI:AKI