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package signer
import (
"crypto/md5"
"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"
"golang.org/x/crypto/ssh"
)
// 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 map[string]string
}
// SignUserKey returns a signed ssh certificate.
func (s *KeySigner) SignUserKey(req *lib.SignRequest) (string, error) {
pubkey, _, _, _, err := ssh.ParseAuthorizedKey([]byte(req.Key))
if err != nil {
return "", 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", req.Principal, time.Now().UTC().Unix()),
ValidBefore: uint64(req.ValidUntil.Unix()),
ValidAfter: uint64(time.Now().UTC().Add(-5 * time.Minute).Unix()),
}
cert.ValidPrincipals = append(cert.ValidPrincipals, req.Principal)
cert.ValidPrincipals = append(cert.ValidPrincipals, s.principals...)
cert.Extensions = s.permissions
if err := cert.SignCert(rand.Reader, s.ca); err != nil {
return "", err
}
marshaled := ssh.MarshalAuthorizedKey(cert)
// Remove the trailing newline.
marshaled = marshaled[:len(marshaled)-1]
log.Printf("Issued cert id: %s principals: %s fp: %s valid until: %s\n", cert.KeyId, cert.ValidPrincipals, fingerprint(pubkey), time.Unix(int64(cert.ValidBefore), 0).UTC())
return string(marshaled), nil
}
func makeperms(perms []string) map[string]string {
if len(perms) > 0 {
m := make(map[string]string)
for _, p := range perms {
m[p] = ""
}
return m
}
return map[string]string{
"permit-X11-forwarding": "",
"permit-agent-forwarding": "",
"permit-port-forwarding": "",
"permit-pty": "",
"permit-user-rc": "",
}
}
// 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: makeperms(conf.Permissions),
}, nil
}
func fingerprint(pubkey ssh.PublicKey) string {
md5String := md5.New()
md5String.Write(pubkey.Marshal())
fp := fmt.Sprintf("% x", md5String.Sum(nil))
return strings.Replace(fp, " ", ":", -1)
}
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