1 // Package key implements epoint key pair generation and handling.
3 // An epoint key is an OpenPGP signing key that contains a self-signed
4 // user id packet which matches
5 // "Issuer (<denomination>)"
7 // "Holder of <issuer fpr> (<denomination>)"
9 // The OpenPGP DSA key material is generated from a random seed using
10 // a deterministic algorithm. (The self-signature is not deterministic
11 // but the key material and thus the fingerprint is.)
12 // This makes it possible to represent an obligation issuer or holder key
13 // pair with a few bits of secret random seed.
14 // (The user id only needs to be set up correctly when the key is uploaded
15 // to the epoint server, it is not required for signing draft documents.)
22 "crypto/openpgp/packet"
30 // TODO: keep denomination only in issuer key?
33 const P = "A4D2B9575C25F0E622B8694387128A793E1AD27D12FFF4B5BA11A37CEFD31C935BCBB0A944581A6E6DA12986FCBA9D666607D71D365C286B9BCB57F6D938BE74982B7D770CE438F03B0A20ABA02E5691458C39D96E6E86AE564176ED1A6DFBAFB6EE7674CC5EDCF9FEB6158471FB3FAB53BA1CE1BA64C5626B9E8585FCEF5D31"
34 const Q = "FFFFFFFFFFFFFFFFFFFF254EAF9E7916D607AAAF"
35 const G = "7EA5C898777BE4BB29DCDC47289E718F7274C9CD7E570D3D552F3B3EE43C3DEF7BA68E57786926520CCAC71DBA13F37C4064395D5AF3334A04ABD8CED5E7FF476C661953936E8ADDE96A39D8C4AC1080A2BE3FE863A24B08BD43827E54AFADA72433704EA3C12E50E5BD08C130C68A1402FC20DA79CFE0DE931C414348D32B10"
37 // Calculate DSA private key from given random seed r
38 func DsaKey(r []byte) *dsa.PrivateKey {
39 priv := new(dsa.PrivateKey)
40 priv.Parameters.P, _ = new(big.Int).SetString(P, 16)
41 priv.Parameters.Q, _ = new(big.Int).SetString(Q, 16)
42 priv.Parameters.G, _ = new(big.Int).SetString(G, 16)
50 // TODO: zero out r and h ?
51 if x.Sign() == 0 || x.Cmp(priv.Q) >= 0 {
57 priv.Y.Exp(priv.G, x, priv.P)
61 // Generate a random DSA private key
62 func RandomDsaKey() (priv *dsa.PrivateKey, err error) {
63 r := make([]byte, sha1.Size)
64 _, err = io.ReadFull(rand.Reader, r)
69 // New returns an openpgp.Entity that contains a fresh DSA private key with a
70 // single identity composed of the given full name, comment and email, any of
71 // which may be empty but must not contain any of "()<>\x00".
72 func New(priv *dsa.PrivateKey, currentTimeSecs int64, name, comment, email string) (e *openpgp.Entity, err error) {
73 uid := packet.NewUserId(name, comment, email)
75 return nil, fmt.Errorf("NewEntity: invalid argument: user id field contained invalid characters")
77 t := uint32(currentTimeSecs)
79 PrimaryKey: packet.NewDSAPublicKey(t, &priv.PublicKey, false /* not a subkey */ ),
80 PrivateKey: packet.NewDSAPrivateKey(t, priv, false /* not a subkey */ ),
81 Identities: make(map[string]*openpgp.Identity),
84 e.Identities[uid.Id] = &openpgp.Identity{
87 SelfSignature: &packet.Signature{
89 SigType: packet.SigTypePositiveCert,
90 PubKeyAlgo: packet.PubKeyAlgoDSA,
92 IsPrimaryId: &isPrimaryId,
96 IssuerKeyId: &e.PrimaryKey.KeyId,
102 // Issuer generates a key for obligation issuer clients from random seed r
103 func Issuer(r []byte, denomination string) (e *openpgp.Entity, err error) {
104 return New(DsaKey(r), 0, "Issuer", denomination, "")
106 // Holder generates a key for obligation holder clients from random seed r
107 func Holder(r []byte, issuer, denomination string) (e *openpgp.Entity, err error) {
108 return New(DsaKey(r), 0, "Holder of "+issuer, denomination, "")
111 // Check the issuer and denomination associated with the given pgp key
112 func Check(e *openpgp.Entity) (isIssuer bool, issuer, denomination string, err error) {
113 // allow multiple identities, use the first one that looks like an epoint uid
114 for _, id := range e.Identities {
115 denomination = id.UserId.Comment
116 if id.UserId.Name == "Issuer" {
118 issuer = fmt.Sprintf("%X", e.PrimaryKey.Fingerprint)
121 const prefix = "Holder of "
122 if id.UserId.Name[:len(prefix)] == prefix {
123 issuer = id.UserId.Name[len(prefix):]
127 err = fmt.Errorf("Check: no valid userid was found")