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/*
Package dsse implements the Dead Simple Signing Envelope (DSSE)
https://github.com/secure-systems-lab/dsse
*/
package dsse
import (
"context"
"encoding/base64"
"errors"
)
// ErrNoSigners indicates that no signer was provided.
var ErrNoSigners = errors.New("no signers provided")
// EnvelopeSigner creates signed Envelopes.
type EnvelopeSigner struct {
providers []SignerVerifier
}
/*
NewEnvelopeSigner creates an EnvelopeSigner that uses 1+ Signer algorithms to
sign the data. Creates a verifier with threshold=1, at least one of the
providers must validate signatures successfully.
*/
func NewEnvelopeSigner(p ...SignerVerifier) (*EnvelopeSigner, error) {
return NewMultiEnvelopeSigner(1, p...)
}
/*
NewMultiEnvelopeSigner creates an EnvelopeSigner that uses 1+ Signer
algorithms to sign the data. Creates a verifier with threshold. Threshold
indicates the amount of providers that must validate the envelope.
*/
func NewMultiEnvelopeSigner(threshold int, p ...SignerVerifier) (*EnvelopeSigner, error) {
var providers []SignerVerifier
for _, sv := range p {
if sv != nil {
providers = append(providers, sv)
}
}
if len(providers) == 0 {
return nil, ErrNoSigners
}
return &EnvelopeSigner{
providers: providers,
}, nil
}
/*
SignPayload signs a payload and payload type according to DSSE.
Returned is an envelope as defined here:
https://github.com/secure-systems-lab/dsse/blob/master/envelope.md
One signature will be added for each Signer in the EnvelopeSigner.
*/
func (es *EnvelopeSigner) SignPayload(ctx context.Context, payloadType string, body []byte) (*Envelope, error) {
var e = Envelope{
Payload: base64.StdEncoding.EncodeToString(body),
PayloadType: payloadType,
}
paeEnc := PAE(payloadType, body)
for _, signer := range es.providers {
sig, err := signer.Sign(ctx, paeEnc)
if err != nil {
return nil, err
}
keyID, err := signer.KeyID()
if err != nil {
keyID = ""
}
e.Signatures = append(e.Signatures, Signature{
KeyID: keyID,
Sig: base64.StdEncoding.EncodeToString(sig),
})
}
return &e, nil
}
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