Init must be called before invoking any other operation of the module.
Most types defined here provide several common operations:
t1 .eq( t2 ) Return true iff values t1 and t2 are equal.
t .sexp() Return an S-expression s representing the value of t . Subsequently, the Sexp operation s .pack() will yield an array of bytes containing the value t in SPKI's canonical S-expression form.
t .text() Return a textual representation of the value t ; it is often just the textual representation of the corresponding S-expression.
Hash is the internal representation of hash values, containing an algorithm name alg and then the hash itself as an array of bytes. SPKI entities such as the public key of a principal or a signed certificate are often represented by the hash values of their corresponding S-expressions, where the hash value is later used as a compact way to refer to the original entity. For example, a <principal> is either a <public-key> or a <hash-of-key> , where the latter refers to some instance of the former. Current hash algorithms are \f5"sha1" and \f5"md5. A Hash value can be created from an S-expression representing a SPKI <hash> element by parsehash . It returns nil if the S-expression was ill-formed.
Key represents public and private keys, with an optional associated pre-hash encoding henc , the hash algorithm halg to be used when signing, and an optional list of currently known hashes of the public component of the key itself. SPKI identifies principals and public keys, thus each instance of a principal in the other data structures is represented by a Key giving the corresponding public key, or its hash, or both. Currently the public and private (secret) key values have types defined by keyring-intro (2). A Key value can be created from an S-expression representing a SPKI <public-key> element by parsekey . It returns nil if the S-expression was ill-formed. For a given Key k :
k .ishash() Returns true if k is just a hash of a key, with no public or private components.
k .public() Returns the public key for k , which is simply k if it is already a public key, but if it is a private key, then a new key is returned that has only public components. Public returns a nil value if k is just a hash of a key value.
k .sigalg() Returns the SPKI signature algorithm for the key.
k .hashed( alg ) Return an array of bytes giving the hash of the Key k using algorithm alg . It returns nil if k .ishash() is true, and k has no associated hash value for alg .
k .hashexp( alg ) Similar to hashed , but returns a Hash value instead of the raw data.
Name represents both local and extended names, and simple principals consisting of just a key. The field principal gives the key that defines the name space in which the list of names is interpreted. For simple principles, the list of names is nil. A local name has exactly one name in the list. Two parsing functions convert to Name from S-expressions. Parsename parses a SPKI <name> element: (name [ principal ] name ... ), where principal is either a <public-key> or a <hash> element. Parsecompound accepts either a <name> element as above, or a <public-key> or its <hash> . Both functions return nil if the S-expression is ill-formed.
Subject represents the subjects of SPKI name and authorisation certificates. It has several variants in a pick adt, with suitable fields for each variant:
Subject.P A simple principal: a key .
Subject.N A group of principals or a delayed binding to a principal: a name .
Subject.O The hash of an object.
Subject.KH A keyholder certificate, that says something about a key's holder (represented by a Name ).
Subject.T A threshold subject, used only in authorisation certificates. The n subsidiary subjects are listed in subs ; of those, at least k must sign a request for it to be authorised.
Subject provides the common operations eq , sexp and text , and a further operation:
s .principal() If s is a simple principal or a name, return the Key defining the principal, if known; return nil otherwise.
Subjects appear only as a subsidiary item in certificates and do not have a parsing function.
Cert represents SPKI certificates. There are four variants, represented by a pick adt: Cert.A (authorisation); Cert.KH (keyholder); Cert.O (object); and Cert.N (name). The following fields and operations are common to all variants:
e original S-expression (if created by parsecert ) to allow hashes and signatures to be computed on the SPKI canonical form of the certificate
issuer The simple principal (represented as a name) that issued an authorisation, keyholder or object certificate, or the <issuer-name> of a name certificate (allowing both local and extended names not just simple principals).
subject The Subject of the certificate. Name certificates may not have threshold subjects.
valid Optional restriction on the certificate's validity (see Valid for details).
Name certificates have only the fields above; the others have several more fields:
delegate True iff the certificate carries delegation rights (ie, (propagate) in the S-expression representation).
tag An S-expression that expresses the authority granted by the certificate. The expression "(tag (*))" means `all permissions'.
A Cert value can be created from an S-expression representing a SPKI <cert> element by parsecert . It returns nil if the expression was ill-formed.
SPKI tag expressions, represented internally by Sexprs->Sexpr trees, form a partial order, including the pattern operations (*) , "(* set " ... ), "(* prefix " ... ), "(* range " ... ), and as an extension, "(* suffix " ... ). Given two tag expressions t1 and t2 , tagintersect returns a tag expression representing t1 ∩ t2 ; tagimplies returns true iff tag t1 implies tag t2 : (t1∩t2)=t2. Both functions work correctly when t1 and t2 contain any legal combination of pattern operations.
SPKI structures are converted to a canonical form of S-expression to be hashed or signed (with or without hashing). Hashbytes returns an array of bytes containing the result of hashing array a using hash algorithm alg (either sha1 or md5 ). Hashexp returns an array of bytes containing the hash of the canonical form of expression e using hash algorithm alg .
Signature associates hash , the Hash value of something (eg, a public key) with the result of applying a public-key signature algorithm sa to that hash value. The name of the algorithm has the form
.EX alg[-[encoding-]hash] with up to three subcomponents (separated by dashes), where alg is a public key algorithm such as rsa or dsa , encoding is an optional encoding to apply to the value before signing, and hash is the secure hash algorithm to apply to the encoded value before signing. For example, the usual algorithms for RSA keys are rsa-pkcs1-sha1 and rsa-pkcs1-md5 .Signatures are created by signcert , which signs a SPKI certificate represented by c with key using the signature algorithm sigalg . Key must contain both public and secret (private) components. Any other binary data can be signed by signbytes , which signs arbitrary data represented by an array of bytes a . Both functions apply any encoding and hash algorithms mentioned by sigalg , and return a tuple ( sig , err ). On success, sig refers to a Signature value that can be converted to an S-expression using sig .sexp() and err is nil. On an error, sig is nil and err contains a diagnostic.
A certificate's signature can be checked by checksig . If sig is a valid signature for certificate c , checksig returns nil. If the signature is invalid, checksig returns a diagnostic.