Re: [TLS] BoringSSL's TLS test suite

> -----Original Message-----
> From: TLS [mailto:tls-bounces@ietf.org] On Behalf Of Henrick Hellström
> Sent: Sunday, September 25, 2016 4:35 PM
> To: David Benjamin <davidben@chromium.org>; Adam Langley
> <agl@imperialviolet.org>
> Cc: tls@ietf.org
> Subject: Re: [TLS] BoringSSL's TLS test suite
> 
> On 2016-09-25 23:55, David Benjamin wrote:
> > I believe we are also correct per spec. My interpretation of these
> > documents is that the general AlgorithmIdentifier structure may or may
> > not include parameters. However, whether a given parameter value or
> > omitting parameters altogether is legal is a question for the
> > particular algorithm. It's not overriding but plugging into the general
> framework.
> 
> THe ITU-T X.690 standard for DER might require some close reading to
interpret,
> and this is obviously a topic for debate. I would presume that the use of
> "default" in lower caps in section 11.5, refers to both the DEFAULT and
the
> OPTIONAL keyword:

OPTIONAL and DEFAULT are not the same things.  A DEFAULT value is omitted
but not an OPTIONAL value.  A single field cannot be both OPTIONAL and
DEFAULT.

Jim

> 
>    11.5	Set and sequence components with default value
>    The encoding of a set value or sequence value shall not include an
>    encoding for any component value which is equal to its default value.
> 
> After all, this is the only interpretation that is consistent with the
description in
> section 12.5 of DER as unambiguous.
> 
> Since NULL is always empty, it should be omitted when OPTIONAL, given the
> above interpretation. But is it optional? The 1988 syntax did not feature
> information objects and classes, hence the use of the ANY keyword.
> 
> Luckily the ASN.1 modules were updated in RFC 5912 to modern ASN.1 syntax.
> There you have these declarations:
> 
> --  SIGNATURE-ALGORITHM
> --
> --  Describes the basic properties of a signature algorithm
> --
> --  &id - contains the OID identifying the signature algorithm
> --  &Value - contains a type definition for the value structure of
> --              the signature; if absent, implies that no ASN.1
> --              encoding is performed on the value
> --  &Params - if present, contains the type for the algorithm
> --               parameters; if absent, implies no parameters
> --  &paramPresence - parameter presence requirement
> --  &HashSet - The set of hash algorithms used with this
> --                  signature algorithm
> --  &PublicKeySet - the set of public key algorithms for this
> --                  signature algorithm
> --  &smimeCaps - contains the object describing how the S/MIME
> --              capabilities are presented.
> --
> --  Example:
> --  sig-RSA-PSS SIGNATURE-ALGORITHM ::= {
> --     IDENTIFIER id-RSASSA-PSS
> --     PARAMS TYPE RSASSA-PSS-params ARE required
> --     HASHES { mda-sha1 | mda-md5, ... }
> --     PUBLIC-KEYS { pk-rsa | pk-rsa-pss }
> -- }
> 
> 
> SIGNATURE-ALGORITHM ::= CLASS {
>      &id             OBJECT IDENTIFIER UNIQUE,
>      &Value          OPTIONAL,
>      &Params         OPTIONAL,
>      &paramPresence  ParamOptions DEFAULT absent,
>      &HashSet        DIGEST-ALGORITHM OPTIONAL,
>      &PublicKeySet   PUBLIC-KEY OPTIONAL,
>      &smimeCaps      SMIME-CAPS OPTIONAL
> } WITH SYNTAX {
>      IDENTIFIER &id
>      [VALUE &Value]
>      [PARAMS [TYPE &Params] ARE &paramPresence ]
>      [HASHES &HashSet]
>      [PUBLIC-KEYS &PublicKeySet]
> 
> AlgorithmIdentifier{ALGORITHM-TYPE, ALGORITHM-TYPE:AlgorithmSet} ::=
>          SEQUENCE {
>              algorithm   ALGORITHM-TYPE.&id({AlgorithmSet}),
>              parameters  ALGORITHM-TYPE.
>                     &Params({AlgorithmSet}{@algorithm}) OPTIONAL
>          }
> 
>     pk-rsa PUBLIC-KEY ::= {
>      IDENTIFIER rsaEncryption
>      KEY RSAPublicKey
>      PARAMS TYPE NULL ARE absent
>      -- Private key format not in this module --
>      CERT-KEY-USAGE {digitalSignature, nonRepudiation,
>      keyEncipherment, dataEncipherment, keyCertSign, cRLSign}
>     }
> 
> Hence, the correct encoding is for NULL to be absent.
> 
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