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principal.go
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principal.go
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// Copyright 2015 The Vanadium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package security
import (
"fmt"
"reflect"
"time"
)
// CreatePrincipal returns a Principal that uses 'signer' for all
// private key operations, 'store' for storing blessings bound
// to the Principal and 'roots' for the set of authoritative public
// keys on blessings recognized by this Principal.
//
// If provided 'roots' is nil then the Principal does not trust any
// public keys and all subsequent 'AddToRoots' operations fail.
//
// It returns an error if store.PublicKey does not match signer.PublicKey.
//
// NOTE: v.io/x/ref/lib/testutil/security provides utility methods for creating
// principals for testing purposes.
func CreatePrincipal(signer Signer, store BlessingStore, roots BlessingRoots) (Principal, error) {
if store == nil {
store = errStore{signer.PublicKey()}
}
if roots == nil {
roots = errRoots{}
}
if got, want := store.PublicKey(), signer.PublicKey(); !reflect.DeepEqual(got, want) {
return nil, fmt.Errorf("store's public key: %v does not match signer's public key: %v", got, want)
}
return &principal{signer: signer, store: store, roots: roots}, nil
}
// CreatePrincipalPublicKeyOnly returns a Principal that cannot sign new blessings
// and has only the public key portion of the original key pair used to create
// it.
func CreatePrincipalPublicKeyOnly(publicKey PublicKey, store BlessingStore, roots BlessingRoots) (Principal, error) {
if store == nil {
store = errStore{publicKey}
}
if roots == nil {
roots = errRoots{}
}
return &principal{signer: nil, publicKey: publicKey, store: store, roots: roots}, nil
}
var (
// Every Signer.Sign operation conducted by the principal fills in a
// "purpose" before signing to prevent "type attacks" so that a signature obtained
// for one operation (e.g. Principal.Sign) cannot be re-purposed for another
// operation (e.g. Principal.Bless). If the "Principal" object lives in an
// external "agent" process, this works out well since this other process
// can confidently audit all private key operations.
// For this to work, ALL private key operations by the Principal must
// use a distinct "purpose" and no two "purpose"s should share a prefix
// or suffix.
blessPurpose = []byte(SignatureForBlessingCertificates)
signPurpose = []byte(SignatureForMessageSigning)
dischargePurpose = []byte(SignatureForDischarge)
)
type errStore struct {
key PublicKey
}
func (errStore) Set(Blessings, BlessingPattern) (Blessings, error) {
return Blessings{}, fmt.Errorf("underlying BlessingStore object is nil")
}
func (errStore) ForPeer(peerBlessings ...string) Blessings { return Blessings{} }
func (errStore) SetDefault(blessings Blessings) error {
return fmt.Errorf("underlying BlessingStore object is nil")
}
func (errStore) Default() (Blessings, <-chan struct{}) { return Blessings{}, nil }
func (errStore) PeerBlessings() map[BlessingPattern]Blessings { return nil }
func (errStore) CacheDischarge(Discharge, Caveat, DischargeImpetus) error { return nil }
func (errStore) ClearDischarges(...Discharge) {}
func (errStore) Discharge(Caveat, DischargeImpetus) (d Discharge, t time.Time) { return d, t }
func (errStore) DebugString() string {
return fmt.Errorf("underlying BlessingStore object is nil").Error()
}
func (s errStore) PublicKey() PublicKey { return s.key }
type errRoots struct{}
func (errRoots) Add([]byte, BlessingPattern) error {
return fmt.Errorf("underlying BlessingRoots object is nil")
}
func (errRoots) Recognized([]byte, string) error {
return fmt.Errorf("underlying BlessingRoots object is nil")
}
func (errRoots) Dump() map[BlessingPattern][]PublicKey { return nil }
func (errRoots) DebugString() string {
return fmt.Errorf("underlying BlessingRoots object is nil").Error()
}
type principal struct {
signer Signer
publicKey PublicKey
roots BlessingRoots
store BlessingStore
}
func (p *principal) Bless(key PublicKey, with Blessings, extension string, caveat Caveat, additionalCaveats ...Caveat) (Blessings, error) {
if with.IsZero() || with.isNamelessBlessing() {
return Blessings{}, fmt.Errorf("the Blessings to bless 'with' must have at least one certificate")
}
if !reflect.DeepEqual(with.PublicKey(), p.PublicKey()) {
return Blessings{}, fmt.Errorf("Principal with public key %v cannot extend blessing with public key %v", p.PublicKey(), with.PublicKey())
}
caveats := make([]Caveat, len(additionalCaveats)+1)
copy(caveats, additionalCaveats)
caveats[len(additionalCaveats)] = caveat
cert, err := newUnsignedCertificate(extension, key, caveats...)
if err != nil {
return Blessings{}, err
}
chains := with.chains
newchains := make([][]Certificate, len(chains))
newdigests := make([][]byte, len(chains))
for idx, chain := range chains {
if newchains[idx], newdigests[idx], err = chainCertificate(p.signer, chain, *cert); err != nil {
return Blessings{}, err
}
}
ret := Blessings{
chains: newchains,
publicKey: key,
digests: newdigests,
}
ret.init()
return ret, nil
}
func (p *principal) BlessSelf(name string, caveats ...Caveat) (Blessings, error) {
if p.signer == nil {
return Blessings{}, fmt.Errorf("underlying signer is nil")
}
cert, err := newUnsignedCertificate(name, p.PublicKey(), caveats...)
if err != nil {
return Blessings{}, err
}
chain, digest, err := chainCertificate(p.signer, nil, *cert)
if err != nil {
return Blessings{}, err
}
ret := Blessings{
chains: [][]Certificate{chain},
publicKey: p.PublicKey(),
digests: [][]byte{digest},
}
ret.init()
return ret, nil
}
func (p *principal) Sign(message []byte) (Signature, error) {
if p.signer == nil {
return Signature{}, fmt.Errorf("signing not supported, only public key available")
}
return p.signer.Sign(signPurpose, message)
}
func (p *principal) MintDischarge(forCaveat, caveatOnDischarge Caveat, additionalCaveatsOnDischarge ...Caveat) (Discharge, error) {
if forCaveat.Id != PublicKeyThirdPartyCaveat.Id {
return Discharge{}, fmt.Errorf("cannot mint discharges for %v", forCaveat)
}
id := forCaveat.ThirdPartyDetails().ID()
dischargeCaveats := make([]Caveat, len(additionalCaveatsOnDischarge)+1)
copy(dischargeCaveats, additionalCaveatsOnDischarge)
dischargeCaveats[len(additionalCaveatsOnDischarge)] = caveatOnDischarge
d := PublicKeyDischarge{ThirdPartyCaveatId: id, Caveats: dischargeCaveats}
if err := d.sign(p.signer); err != nil {
return Discharge{}, fmt.Errorf("failed to sign discharge: %v", err)
}
return Discharge{WireDischargePublicKey{d}}, nil
}
func (p *principal) PublicKey() PublicKey {
if p.signer == nil {
return p.publicKey
}
return p.signer.PublicKey()
}
func (p *principal) BlessingStore() BlessingStore {
return p.store
}
func (p *principal) Roots() BlessingRoots {
return p.roots
}