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Copy pathage.go
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238 lines (214 loc) · 7.91 KB
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// Copyright 2019 The age Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package age implements file encryption according to the age-encryption.org/v1
// specification.
//
// For most use cases, use the Encrypt and Decrypt functions with
// X25519Recipient and X25519Identity. If passphrase encryption is required, use
// ScryptRecipient and ScryptIdentity. For compatibility with existing SSH keys
// use the filippo.io/age/agessh package.
//
// Age encrypted files are binary and not malleable. For encoding them as text,
// use the filippo.io/age/armor package.
//
// Key management
//
// Age does not have a global keyring. Instead, since age keys are small,
// textual, and cheap, you are encouraged to generate dedicated keys for each
// task and application.
//
// Recipient public keys can be passed around as command line flags and in
// config files, while secret keys should be stored in dedicated files, through
// secret management systems, or as environment variables.
//
// There is no default path for age keys. Instead, they should be stored at
// application-specific paths. The CLI supports files where private keys are
// listed one per line, ignoring empty lines and lines starting with "#". These
// files can be parsed with ParseIdentities.
//
// When integrating age into a new system, it's recommended that you only
// support X25519 keys, and not SSH keys. The latter are supported for manual
// encryption operations. If you need to tie into existing key management
// infrastructure, you might want to consider implementing your own Recipient
// and Identity.
//
// Backwards compatibility
//
// Files encrypted with a stable version (not alpha, beta, or release candidate)
// of age, or with any v1.0.0 beta or release candidate, will decrypt with any
// later versions of the v1 API. This might change in v2, in which case v1 will
// be maintained with security fixes for compatibility with older files.
//
// If decrypting an older file poses a security risk, doing so might require an
// explicit opt-in in the API.
package age
import (
"crypto/hmac"
"crypto/rand"
"errors"
"fmt"
"io"
"filippo.io/age/internal/format"
"filippo.io/age/internal/stream"
)
// An Identity is passed to Decrypt to unwrap an opaque file key from a
// recipient stanza. It can be for example a secret key like X25519Identity, a
// plugin, or a custom implementation.
//
// Unwrap must return an error wrapping ErrIncorrectIdentity if none of the
// recipient stanzas match the identity, any other error will be considered
// fatal.
//
// Most age API users won't need to interact with this directly, and should
// instead pass Recipient implementations to Encrypt and Identity
// implementations to Decrypt.
type Identity interface {
Unwrap(stanzas []*Stanza) (fileKey []byte, err error)
}
var ErrIncorrectIdentity = errors.New("incorrect identity for recipient block")
// A Recipient is passed to Encrypt to wrap an opaque file key to one or more
// recipient stanza(s). It can be for example a public key like X25519Recipient,
// a plugin, or a custom implementation.
//
// Most age API users won't need to interact with this directly, and should
// instead pass Recipient implementations to Encrypt and Identity
// implementations to Decrypt.
type Recipient interface {
Wrap(fileKey []byte) ([]*Stanza, error)
}
// A Stanza is a section of the age header that encapsulates the file key as
// encrypted to a specific recipient.
//
// Most age API users won't need to interact with this directly, and should
// instead pass Recipient implementations to Encrypt and Identity
// implementations to Decrypt.
type Stanza struct {
Type string
Args []string
Body []byte
}
const fileKeySize = 16
const streamNonceSize = 16
// Encrypt encrypts a file to one or more recipients.
//
// Writes to the returned WriteCloser are encrypted and written to dst as an age
// file. Every recipient will be able to decrypt the file.
//
// The caller must call Close on the WriteCloser when done for the last chunk to
// be encrypted and flushed to dst.
func Encrypt(dst io.Writer, recipients ...Recipient) (io.WriteCloser, error) {
if len(recipients) == 0 {
return nil, errors.New("no recipients specified")
}
// As a best effort, prevent an API user from generating a file that the
// ScryptIdentity will refuse to decrypt. This check can't unfortunately be
// implemented as part of the Recipient interface, so it lives as a special
// case in Encrypt.
for _, r := range recipients {
if _, ok := r.(*ScryptRecipient); ok && len(recipients) != 1 {
return nil, errors.New("an ScryptRecipient must be the only one for the file")
}
}
fileKey := make([]byte, fileKeySize)
if _, err := rand.Read(fileKey); err != nil {
return nil, err
}
hdr := &format.Header{}
for i, r := range recipients {
stanzas, err := r.Wrap(fileKey)
if err != nil {
return nil, fmt.Errorf("failed to wrap key for recipient #%d: %v", i, err)
}
for _, s := range stanzas {
hdr.Recipients = append(hdr.Recipients, (*format.Stanza)(s))
}
}
if mac, err := headerMAC(fileKey, hdr); err != nil {
return nil, fmt.Errorf("failed to compute header MAC: %v", err)
} else {
hdr.MAC = mac
}
if err := hdr.Marshal(dst); err != nil {
return nil, fmt.Errorf("failed to write header: %v", err)
}
nonce := make([]byte, streamNonceSize)
if _, err := rand.Read(nonce); err != nil {
return nil, err
}
if _, err := dst.Write(nonce); err != nil {
return nil, fmt.Errorf("failed to write nonce: %v", err)
}
return stream.NewWriter(streamKey(fileKey, nonce),
7EBA
dst)
}
// NoIdentityMatchError is returned by Decrypt when none of the supplied
// identities match the encrypted file.
type NoIdentityMatchError struct {
// Errors is a slice of all the errors returned to Decrypt by the Unwrap
// calls it made. They all wrap ErrIncorrectIdentity.
Errors []error
}
func (*NoIdentityMatchError) Error() string {
return "no identity matched any of the recipients"
}
// Decrypt decrypts a file encrypted to one or more identities.
//
// It returns a Reader reading the decrypted plaintext of the age file read
// from src. All identities will be tried until one successfully decrypts the file.
func Decrypt(src io.Reader, identities ...Identity) (io.Reader, error) {
if len(identities) == 0 {
return nil, errors.New("no identities specified")
}
hdr, payload, err := format.Parse(src)
if err != nil {
return nil, fmt.Errorf("failed to read header: %v", err)
}
stanzas := make([]*Stanza, 0, len(hdr.Recipients))
for _, s := range hdr.Recipients {
stanzas = append(stanzas, (*Stanza)(s))
}
errNoMatch := &NoIdentityMatchError{}
var fileKey []byte
for _, id := range identities {
fileKey, err = id.Unwrap(stanzas)
if errors.Is(err, ErrIncorrectIdentity) {
errNoMatch.Errors = append(errNoMatch.Errors, err)
continue
}
if err != nil {
return nil, err
}
break
}
if fileKey == nil {
return nil, errNoMatch
}
if mac, err := headerMAC(fileKey, hdr); err != nil {
return nil, fmt.Errorf("failed to compute header MAC: %v", err)
} else if !hmac.Equal(mac, hdr.MAC) {
return nil, errors.New("bad header MAC")
}
nonce := make([]byte, streamNonceSize)
if _, err := io.ReadFull(payload, nonce); err != nil {
return nil, fmt.Errorf("failed to read nonce: %v", err)
}
return stream.NewReader(streamKey(fileKey, nonce), payload)
}
// multiUnwrap is a helper that implements Identity.Unwrap in terms of a
// function that unwraps a single recipient stanza.
func multiUnwrap(unwrap func(*Stanza) ([]byte, error), stanzas []*Stanza) ([]byte, error) {
for _, s := range stanzas {
fileKey, err := unwrap(s)
if errors.Is(err, ErrIncorrectIdentity) {
// If we ever start returning something interesting wrapping
// ErrIncorrectIdentity, we should let it make its way up through
// Decrypt into NoIdentityMatchError.Errors.
continue
}
if err != nil {
return nil, err
}
return fileKey, nil
}
return nil, ErrIncorrectIdentity
}