package signer import ( "crypto/rand" "fmt" "log" "strings" "time" "go4.org/wkfs" _ "go4.org/wkfs/gcs" // Register "/gcs/" as a wkfs. "github.com/nsheridan/cashier/lib" "github.com/nsheridan/cashier/server/config" "github.com/nsheridan/cashier/server/store" "github.com/stripe/krl" "golang.org/x/crypto/ssh" ) var ( defaultPermissions = map[string]string{ "permit-X11-forwarding": "", "permit-agent-forwarding": "", "permit-port-forwarding": "", "permit-pty": "", "permit-user-rc": "", } ) // KeySigner does the work of signing a ssh public key with the CA key. type KeySigner struct { ca ssh.Signer validity time.Duration principals []string permissions []string } func (s *KeySigner) setPermissions(cert *ssh.Certificate) { cert.CriticalOptions = make(map[string]string) cert.Extensions = make(map[string]string) for _, perm := range s.permissions { if strings.Contains(perm, "=") { opt := strings.Split(perm, "=") cert.CriticalOptions[strings.TrimSpace(opt[0])] = strings.TrimSpace(opt[1]) } else { cert.Extensions[perm] = "" } } if len(cert.Extensions) == 0 { cert.Extensions = defaultPermissions } } // SignUserKey returns a signed ssh certificate. func (s *KeySigner) SignUserKey(req *lib.SignRequest, username string) (*ssh.Certificate, error) { pubkey, _, _, _, err := ssh.ParseAuthorizedKey([]byte(req.Key)) if err != nil { return nil, err } expires := time.Now().UTC().Add(s.validity) if req.ValidUntil.After(expires) { req.ValidUntil = expires } cert := &ssh.Certificate{ CertType: ssh.UserCert, Key: pubkey, KeyId: fmt.Sprintf("%s_%d", username, time.Now().UTC().Unix()), ValidAfter: uint64(time.Now().UTC().Add(-5 * time.Minute).Unix()), ValidBefore: uint64(req.ValidUntil.Unix()), ValidPrincipals: []string{username}, } cert.ValidPrincipals = append(cert.ValidPrincipals, s.principals...) s.setPermissions(cert) if err := cert.SignCert(rand.Reader, s.ca); err != nil { return nil, err } log.Printf("Issued cert id: %s principals: %s fp: %s valid until: %s\n", cert.KeyId, cert.ValidPrincipals, ssh.FingerprintSHA256(pubkey), time.Unix(int64(cert.ValidBefore), 0).UTC()) return cert, nil } // GenerateRevocationList returns an SSH key revocation list (KRL). func (s *KeySigner) GenerateRevocationList(certs []*store.CertRecord) ([]byte, error) { revoked := &krl.KRLCertificateSection{ CA: s.ca.PublicKey(), } ids := krl.KRLCertificateKeyID{} for _, c := range certs { ids = append(ids, c.KeyID) } revoked.Sections = append(revoked.Sections, &ids) k := &krl.KRL{ Sections: []krl.KRLSection{revoked}, } return k.Marshal(rand.Reader) } // New creates a new KeySigner from the supplied configuration. func New(conf *config.SSH) (*KeySigner, error) { data, err := wkfs.ReadFile(conf.SigningKey) if err != nil { return nil, fmt.Errorf("unable to read CA key %s: %v", conf.SigningKey, err) } key, err := ssh.ParsePrivateKey(data) if err != nil { return nil, fmt.Errorf("unable to parse CA key: %v", err) } validity, err := time.ParseDuration(conf.MaxAge) if err != nil { return nil, fmt.Errorf("error parsing duration '%s': %v", conf.MaxAge, err) } return &KeySigner{ ca: key, validity: validity, principals: conf.AdditionalPrincipals, permissions: conf.Permissions, }, nil }