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sign.go
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sign.go
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package sign
import (
"encoding/json"
"errors"
"fmt"
"io/ioutil"
gossh "github.com/coreos/fleet/Godeps/_workspace/src/code.google.com/p/gosshnew/ssh"
gosshagent "github.com/coreos/fleet/Godeps/_workspace/src/code.google.com/p/gosshnew/ssh/agent"
log "github.com/coreos/fleet/Godeps/_workspace/src/github.com/golang/glog"
"github.com/coreos/fleet/pkg"
"github.com/coreos/fleet/ssh"
)
const DefaultAuthorizedKeysFile = "~/.ssh/authorized_keys"
// SignatureSet contains a set of SSH signatures for a blob of data, and is named by a Tag.
type SignatureSet struct {
Tag string
Signatures []*gossh.Signature
}
// SignatureCreator provides the ability to sign a blob of data with multiple SSH public keys, contained in the keyring
type SignatureCreator struct {
keyring gosshagent.Agent
}
// NewSignatureCreator instantiates a SignatureCreator with the given keyring
func NewSignatureCreator(keyring gosshagent.Agent) *SignatureCreator {
return &SignatureCreator{keyring}
}
// NewSignatureCreatorFromSSHAgent return a SignatureCreator which uses the local ssh-agent as its keyring
func NewSignatureCreatorFromSSHAgent() (*SignatureCreator, error) {
keyring, err := ssh.SSHAgentClient()
if err != nil {
return nil, err
}
return &SignatureCreator{keyring}, nil
}
// Sign generates a SignatureSet for the given data, labelled by the supplied tag. It returns a *SignatureSet and any error encountere
func (sc *SignatureCreator) Sign(tag string, data []byte) (*SignatureSet, error) {
if sc.keyring == nil {
return nil, errors.New("signature creator is uninitialized")
}
sigs := make([]*gossh.Signature, 0)
keys, err := sc.keyring.List()
if err != nil {
return nil, err
}
if len(keys) == 0 {
return nil, errors.New("signature creator keyring is empty")
}
for _, k := range keys {
sig, err := sc.keyring.Sign(k, data)
if err != nil {
return nil, err
}
sigs = append(sigs, sig)
}
return &SignatureSet{tag, sigs}, nil
}
type SignatureVerifier struct {
// keys is used to verify signing, created when needed
pubkeys []gossh.PublicKey
}
func NewSignatureVerifier() *SignatureVerifier {
return &SignatureVerifier{}
}
// NewSignatureVerifierFromSSHAgent return SignatureVerifier which uses public keys in the local ssh-agent to verify signatures
func NewSignatureVerifierFromSSHAgent() (*SignatureVerifier, error) {
keyring, err := ssh.SSHAgentClient()
if err != nil {
return nil, err
}
return NewSignatureVerifierFromKeyring(keyring)
}
// NewSignatureVerifierFromKeyring creates a SignatureVerifier
// which uses public keys from the given keyring to verify signatures
func NewSignatureVerifierFromKeyring(keyring gosshagent.Agent) (*SignatureVerifier, error) {
keys, err := keyring.List()
if err != nil {
return nil, err
}
pubkeys := make([]gossh.PublicKey, len(keys))
for i, k := range keys {
pubkeys[i] = k
}
return &SignatureVerifier{pubkeys}, nil
}
// NewSignatureVerifierFromAuthorizedKeysFile creates a
// SignatureVerifier which uses public keys from the specified
// authorized_keys file to verify signatures
func NewSignatureVerifierFromAuthorizedKeysFile(filepath string) (*SignatureVerifier, error) {
out, err := ioutil.ReadFile(pkg.ParseFilepath(filepath))
if err != nil {
return nil, err
}
pubkeys, err := parseAuthorizedKeys(out)
if err != nil {
return nil, err
}
if len(pubkeys) == 0 {
return nil, errors.New("no authorized keys found in file")
}
return &SignatureVerifier{pubkeys}, nil
}
// Verify verifies that at least one of the signatures in the provided
// SignatureSet is a valid signature of the given data blob.
func (sv *SignatureVerifier) Verify(data []byte, s *SignatureSet) (bool, error) {
if sv.pubkeys == nil {
return false, errors.New("signature verifier is uninitialized")
}
for _, authKey := range sv.pubkeys {
// Manually coerce the keys provided by the agent to PublicKeys,
// since gosshnew does not want to do it for us and agent.Keys are unable to Verify
key, err := gossh.ParsePublicKey(authKey.Marshal())
if err != nil {
log.Errorf("Unable to use SSH key: %v", err)
continue
}
for _, sign := range s.Signatures {
if err := key.Verify(data, sign); err == nil {
return true, nil
}
}
}
return false, nil
}
func parseAuthorizedKeys(in []byte) ([]gossh.PublicKey, error) {
pubkeys := make([]gossh.PublicKey, 0)
for len(in) > 0 {
pubkey, _, _, rest, err := gossh.ParseAuthorizedKey(in)
if err != nil {
return nil, err
}
in = rest
pubkeys = append(pubkeys, pubkey)
}
return pubkeys, nil
}
func marshal(obj interface{}) ([]byte, error) {
encoded, err := json.Marshal(obj)
if err == nil {
return encoded, nil
}
return nil, fmt.Errorf("unable to JSON-serialize object: %s", err)
}