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apk/signature: remove support for creating new SHA1 signatures #1496

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apk/signature: remove support for creating new SHA1 signatures #1496

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4 changes: 4 additions & 0 deletions pkg/apk/signature/rsa.go
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Original file line number Diff line number Diff line change
Expand Up @@ -21,11 +21,15 @@ var (
errDigestLength = errors.New("digest has unexpected length")
errNoPassphrase = errors.New("key is encrypted but no passphrase was provided")
errNoRSAKey = errors.New("key is not an RSA key")
errWeakDigest = errors.New("creating sha1 signatures not supported")
)

// RSASignDigest signs the provided message digest. The key file must
// be in the PEM format and can either be encrypted or not.
func RSASignDigest(digest []byte, digestType crypto.Hash, keyFile, passphrase string) ([]byte, error) {
if digestType == crypto.SHA1 {
return nil, errWeakDigest
}
if len(digest) != digestType.Size() {
return nil, errDigestLength
}
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37 changes: 4 additions & 33 deletions pkg/apk/signature/sign.go
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Original file line number Diff line number Diff line change
Expand Up @@ -46,54 +46,25 @@ func SignIndex(ctx context.Context, signingKey string, indexFile string) error {

log.Infof("signing index %s with key %s", indexFile, signingKey)

// Unfortunately apk-tools checks signatures until the first one passes, and skips the rest.
// And golang sorts its reads & writes in lexical order only. Thus indexes will be
// validated with SHA1 only by apk-tools whilst RSA (SHA1) signature is present.
//
// An incremental WriteTargz would allow to write out strongest hash first. Or a MergeFS
// implementation the maintains relative order.
//
// Done:
// Step 0) apk-tools supports RSA256 since 2017
// Step 1) Upgrade all deployments of melange/go-apk with verification support for RSA256
// This PR:
// Step 2) Turn on RSA256 signatures, with RSA escape hatch
// Next:
// Step 3) Remove RSA escape hatch

filename := "RSA256"
digestType := crypto.SHA256

if digest, ok := os.LookupEnv("SIGNING_DIGEST"); ok {
switch digest {
case "SHA256":
case "SHA1":
filename = "RSA"
digestType = crypto.SHA1
default:
return fmt.Errorf("unsupported SIGNING_DIGEST")
}
}

indexData, err := os.ReadFile(indexFile)
if err != nil {
return fmt.Errorf("unable to read index for signing: %w", err)
}

sigFS := memfs.New()
indexDigest, err := HashData(indexData, digestType)
indexDigest, err := HashData(indexData, crypto.SHA256)
if err != nil {
return err
}

sigData, err := RSASignDigest(indexDigest, digestType, signingKey, "")
sigData, err := RSASignDigest(indexDigest, crypto.SHA256, signingKey, "")
if err != nil {
return fmt.Errorf("unable to sign index: %w", err)
}

log.Infof("appending signature %s to index %s", filename, indexFile)
log.Infof("appending signature RSA256 to index %s", indexFile)

if err := sigFS.WriteFile(fmt.Sprintf(".SIGN.%s.%s.pub", filename, filepath.Base(signingKey)), sigData, 0644); err != nil {
if err := sigFS.WriteFile(fmt.Sprintf(".SIGN.RSA256.%s.pub", filepath.Base(signingKey)), sigData, 0644); err != nil {
return fmt.Errorf("unable to append signature: %w", err)
}

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