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zipmeta.go
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/
zipmeta.go
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//
// Copyright (c) SAS Institute Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
package signappx
import (
"crypto/hmac"
"errors"
"fmt"
"io"
"github.com/sassoftware/relic/v8/lib/zipslicer"
)
func verifyMeta(r io.ReaderAt, size int64, sig *AppxSignature, skipDigests bool) error {
dir, err := zipslicer.Read(r, size)
if err != nil {
return err
}
sigIdx := -1
for i, f := range dir.File {
if f.Name == appxSignature {
sigIdx = i
} else if sigIdx >= 0 {
return errors.New("zip elements out of order")
}
}
// AXPC is a hash of everything except the central directory and signature file
axpc := sig.Hash.New()
sink := io.Writer(axpc)
if skipDigests {
sink = nil
}
// AXCD is a hash of the zip central directory with the signature file removed
axcd := sig.Hash.New()
if err := dir.Truncate(sigIdx, sink, axcd); err != nil {
return fmt.Errorf("verifying zip metadata: %w", err)
}
if !skipDigests {
calc := axpc.Sum(nil)
if expected := sig.HashValues["AXPC"]; !hmac.Equal(calc, expected) {
return fmt.Errorf("appx digest mismatch for zip contents: calculated %x != found %x", calc, expected)
}
}
calc := axcd.Sum(nil)
if expected := sig.HashValues["AXCD"]; !hmac.Equal(calc, expected) {
return fmt.Errorf("appx digest mismatch for zip directory: calculated %x != found %x", calc, expected)
}
return nil
}