Re: World's smallest well-formed certificate

$ openssl x509 -in smallest.crt -text
Certificate:
    Data:
        Version: 1 (0x0)
        Serial Number: 0 (0x0)
    Signature Algorithm: 0.0
        Issuer: 
        Validity
            Not Before: May 18 00:00:00 2016 GMT
            Not After : May 18 00:00:00 2017 GMT
        Subject: 
        Subject Public Key Info:
            Public Key Algorithm: 0.0
            Unable to load Public Key
140735154757712:error:0609E09C:digital envelope routines:PKEY_SET_TYPE:unsupported algorithm:p_lib.c:231:
140735154757712:error:0B07706F:x509 certificate routines:X509_PUBKEY_get:unsupported algorithm:x_pubkey.c:148:
    Signature Algorithm: 0.0
-----BEGIN CERTIFICATE-----
MEAwNgIBADADBgEAMAAwHhcNMTYwNTE4MDAwMDAwWhcNMTcwNTE4MDAwMDAwWjAA
MAgwAwYBAAMBADADBgEAAwEA
-----END CERTIFICATE——

> On 18 May 2016, at 4:01 PM, Erwann Abalea <[email protected]> wrote:
> 
> Bonjour,
> 
> Your examples have serial numbers encoded with a zero length, this is not DER compliant.
> The Name type used for issuer and subject is an unconstrained SEQUENCE OF, so in theory it can be empty and be well-formed (from a DER point of view).
> 
> My proposal, 66 octets:
> -----BEGIN CERTIFICATE-----
> MEAwNgIBADADBgEAMAAwHhcNMTYwNTE4MDAwMDAwWhcNMTcwNTE4MDAwMDAwWjAA
> MAgwAwYBAAMBADADBgEAAwEA
> -----END CERTIFICATE-----
> 
> 
> 2016-05-18 11:25 GMT+02:00 Rob Stradling <[email protected] <mailto:[email protected]>>:
> Hi Sean.  I can get OpenSSL to not barf in 99 bytes...
> 
> $ echo "-----BEGIN CERTIFICATE-----
> MGEwVwIAMAMGAQAwCTEHMAUGAQATADAeFw0xNjA1MTgwMDAwMDBaFw0xNzA1MTgw
> MDAwMDBaMAkxBzAFBgEAEwAwGDANBgkqhkiG9w0BAQEFAAMHADAEAgACADADBgEA
> AwEA
> -----END CERTIFICATE-----" | openssl x509 -text -noout
> Certificate:
>     Data:
>         Version: 1 (0x0)
>         Serial Number: 0 (0x0)
>     Signature Algorithm: 0.0
>         Issuer: 0.0=
>         Validity
>             Not Before: May 18 00:00:00 2016 GMT
>             Not After : May 18 00:00:00 2017 GMT
>         Subject: 0.0=
>         Subject Public Key Info:
>             Public Key Algorithm: rsaEncryption
>                 Public-Key: (0 bit)
>                 Modulus: 0
>                 Exponent: 0
>     Signature Algorithm: 0.0
> 
> 
> I see what you mean about barfing on a "malformed" public key.  This was my first attempt...
> 
> $ echo "-----BEGIN CERTIFICATE-----
> MFEwRwIAMAMGAQAwCTEHMAUGAQATADAeFw0xNjA1MTgwMDAwMDBaFw0xNzA1MTgw
> MDAwMDBaMAkxBzAFBgEAEwAwCDADBgEAAwEAMAMGAQADAQA=
> -----END CERTIFICATE-----" | openssl x509 -text -noout
> Certificate:
>     Data:
>         Version: 1 (0x0)
>         Serial Number: 0 (0x0)
>     Signature Algorithm: 0.0
>         Issuer: 0.0=
>         Validity
>             Not Before: May 18 00:00:00 2016 GMT
>             Not After : May 18 00:00:00 2017 GMT
>         Subject: 0.0=
>         Subject Public Key Info:
>             Public Key Algorithm: 0.0
>             Unable to load Public Key
> 3073144508 <tel:3073144508>:error:0609E09C:digital envelope routines:PKEY_SET_TYPE:unsupported algorithm:p_lib.c:231:
> 3073144508 <tel:3073144508>:error:0B07706F:x509 certificate routines:X509_PUBKEY_get:unsupported algorithm:x_pubkey.c:148:
>     Signature Algorithm: 0.0
> 
> P.S. OpenSSL barfs on an RDN Attribute of type NULL, so I used a zero-length PrintableString instead.
> 
> On 18/05/16 08:29, Sean Leonard wrote:
> I'm working on a problem that involves the DER encoding of the smallest
> well-formed (yet pathological) certificate. How many octets can the
> world's smallest well-formed certificate be?
> 
> A Certificate is a SEQUENCE of TBSCertificate, AlgorithmIdentifier, and
> BIT STRING (the signature). The world's smallest certificate would be
> version = 1 (therefore omitted), a serial number of 0, a hypothetical
> signature (AlgorithmIdentifier) that has the world's smallest object
> identifier (0.0) and no parameters, an issuer Name (distinguished name)
> that has one RDN that has one Attribute whose type is the world's
> smallest object identifier (0.0) and whose value is the ASN.1's smallest
> value (NULL), with proper validity times, the same or similar smallest
> subject Name, a well-formed SubjectPublicKeyInfo, and none of the
> optional fields: issuerUniqueID, subjectUniqueID, and extensions.
> 
> By "well-formed", I mean that an ASN.1 '88 parser (i.e., one that does
> not enforce information object classes) will parse it (including the BIT
> STRING contents) and not barf. Such a certificate could not possibly be
> "valid", since the signature block would not be a real digital signature.
> 
> Sean
> 
> (PS For those who want to know "why", it's because I am trying to test
> some assumptions about how small a certificate can be.)
> 
> -- 
> Rob Stradling
> Senior Research & Development Scientist
> COMODO - Creating Trust Online
> 
> 
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> 
> 
> 
> -- 
> Erwann.
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