Inferno's SPKI(2 )

NAME

SPKI: Cert, Hash, Key, Name, Seqel, Signature, Subject, Toplev, Valid - simple public key infrastructure

SYNOPSIS

include "bufio.m";
include "sexprs.m";
include "keyring.m";
include "spki.m";
spki := load SPKI SPKI->PATH;

Hash: adt {
    alg:    string;
    hash:   array of byte;

    sexp:   fn(h: self ref Hash): ref Sexprs->Sexp;
    text:   fn(h: self ref Hash): string;
    eq:     fn(h1: self ref Hash, h2: ref Hash): int;
};

Key: adt {
    pk:     ref Keyring->PK;    # either pk/sk or hash might be nil
    sk:     ref Keyring->SK;
    nbits:  int;
    halg:   string;             # basic signature hash algorithm
    henc:   string;             # pre-signature encoding
    hash:   list of ref Hash;

    hashed:  fn(k: self ref Key, alg: string): array of byte;
    hashexp: fn(k: self ref Key, alg: string): ref Hash;
    public:  fn(k: self ref Key): ref Key;
    sigalg:  fn(k: self ref Key): string;
    text:    fn(k: self ref Key): string;
    sexp:    fn(k: self ref Key): ref Sexprs->Sexp;
    eq:      fn(k1: self ref Key, k2: ref Key): int;
};

Name: adt {
    principal:  ref Key;
    names:  list of string;

    isprincipal: fn(n: self ref Name): int;
    local:    fn(n: self ref Name): ref Name;
    islocal:  fn(n: self ref Name): int;
    isprefix: fn(n1: self ref Name, n2: ref Name): int;
    text:     fn(n: self ref Name): string;
    sexp:     fn(n: self ref Name): ref Sexprs->Sexp;
    eq:       fn(n1: self ref Name, n2: ref Name): int;
};

Cert: adt {
    e:        ref Sexprs->Sexp;   # S-expression, if originally parsed
    issuer:   ref Name;
    subject:  ref Subject;
    valid:    ref Valid;
    pick {
    A or KH or O => # auth, keyholder or object
        delegate:   int;
        tag:        ref Sexprs->Sexp;
    N =>    # name
    }

    text:     fn(c: self ref Cert): string;
    sexp:     fn(c: self ref Cert): ref Sexprs->Sexp;
};

Subject: adt {
    pick{
    P =>
        key:    ref Key;
    N =>
        name:   ref Name;
    O =>
        hash:   ref Hash;
    KH =>
        holder: ref Name;
    T =>
        k, n:   int;
        subs:   cyclic list of ref Subject;
    }

    eq:     fn(s1: self ref Subject, s2: ref Subject): int;
    principal:  fn(s: self ref Subject): ref Key;
    text:   fn(s: self ref Subject): string;
    sexp:   fn(s: self ref Subject): ref Sexprs->Sexp;
};

Signature: adt {
    hash:   ref Hash;
    key:    ref Key;    # find by hash if necessary
    sa:     string;     # alg[-[encoding-]hash
    sig:    list of (string, array of byte);

    algs:   fn(s: self ref Signature): (string, string, string);
    sexp:   fn(s: self ref Signature): ref Sexprs->Sexp;
    text:   fn(s: self ref Signature): string;
};

Seqel: adt {
    pick{
    C =>
        c: ref Cert;
    K =>
        k: ref Key;
    O =>
        op: string;
        args: list of ref Sexprs->Sexp;
    S =>
        sig: ref Signature;
    E =>
        exp:    ref Sexprs->Sexp;
    }

    sexp:   fn(se: self ref Seqeql): ref Sexprs->Sexp;
    text:   fn(se: self ref Seqel): string;
};

Valid: adt {
    notbefore:  string;
    notafter:   string;

    intersect:  fn(a: self Valid, b: Valid): (int, Valid);
    text:   fn(a: self Valid): string;
    sexp:   fn(a: self Valid): ref Sexprs->Sexp;
};

Toplev: adt {
    pick {
    C =>
        v:  ref Cert;
    Sig =>
        v:  ref Signature;
    K =>
        v:  ref Key;
    Seq =>
        v:  list of ref Seqel;
    }

    sexp:   fn(t: self ref Toplev): ref Sexprs->Sexp;
    text:   fn(t: self ref Toplev): string;
};

init:   fn();
date2epoch: fn(s: string): int; # YYYY-MM-DD_HH:MM:SS
epoch2date: fn(t: int): string;
time2secs:  fn(s: string): int; # HH:MM:SS
secs2time:  fn(t: int): string;
sigalgs:    fn(spec: string): (string, string, string);

# parse structures
parse:      fn(s: ref Sexprs->Sexp): (ref Toplev, string);
parseseq:   fn(s: ref Sexprs->Sexp): list of ref Seqel;
parsecert:  fn(s: ref Sexprs->Sexp): ref Cert;
parsesig:   fn(s: ref Sexprs->Sexp): ref Signature;
parsename:  fn(s: ref Sexprs->Sexp): ref Name;
parsekey:   fn(s: ref Sexprs->Sexp): ref Key;
parsehash:  fn(s: ref Sexprs->Sexp): ref Hash;
parsecompound:  fn(s: ref Sexprs->Sexp): ref Name;
parsevalid: fn(s: ref Sexprs->Sexp): ref Valid;

# signature checking
checksig:   fn(c: ref Cert, sig: ref Signature): string;
sig2icert:  fn(sig: ref Signature, signer: string, exp: int): ref Keyring->Certificate;

# signature making
signcert:   fn(c: ref Cert, sigalg: string, key: ref Key):
                 (ref Signature, string);
signbytes:  fn(a: array of byte, sigalg: string, key: ref Key):
                 (ref Signature, string);

# tags
maketag:    fn(e: ref Sexprs->Sexp): ref Sexprs->Sexp;
tagintersect:  fn(t1: ref Sexprs->Sexp, t2: ref Sexprs->Sexp):
                 ref Sexprs->Sexp;
tagimplies: fn(t1: ref Sexprs->Sexp, t2: ref Sexprs->Sexp): int;

# hash canonical s-expression
hashbytes:  fn(a: array of byte, alg: string): array of byte;
hashexp:    fn(e: ref Sexprs->Sexp, alg: string): array of byte;

DESCRIPTION

SPKI provides data types and operations to help build implementations of the Simple Public Key Infrastructure (SPKI). It provides types for hash values, public and private keys, local and extended names, principals and compound principles, certificates, validity periods, signatures, and proof sequences. It also provides operations on authorisation tags. Externally, SPKI represents all such things as particular forms of S-expression, internally represented using Sexprs->Sexp from sexprs(2).

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 "sha1" and "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

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.

SOURCE

/appl/lib/spki.b

SEE ALSO

bufio(2), sexprs(2), spki-verifier(2)

SPKI(2 ) Rev: Tue Mar 31 02:42:39 GMT 2015