| // Copyright 2018 Google LLC |
| // |
| // 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 mac |
| |
| import ( |
| "fmt" |
| |
| "github.com/google/tink/go/core/cryptofmt" |
| "github.com/google/tink/go/core/primitiveset" |
| "github.com/google/tink/go/core/registry" |
| "github.com/google/tink/go/keyset" |
| "github.com/google/tink/go/tink" |
| tinkpb "github.com/google/tink/go/proto/tink_go_proto" |
| ) |
| |
| // New creates a MAC primitive from the given keyset handle. |
| func New(h *keyset.Handle) (tink.MAC, error) { |
| return NewWithKeyManager(h, nil /*keyManager*/) |
| } |
| |
| // NewWithKeyManager creates a MAC primitive from the given keyset handle and a custom key manager. |
| // Deprecated: register the KeyManager and use New above. |
| func NewWithKeyManager(h *keyset.Handle, km registry.KeyManager) (tink.MAC, error) { |
| ps, err := h.PrimitivesWithKeyManager(km) |
| if err != nil { |
| return nil, fmt.Errorf("mac_factory: cannot obtain primitive set: %s", err) |
| } |
| |
| return newWrappedMAC(ps) |
| } |
| |
| // wrappedMAC is a MAC implementation that uses the underlying primitive set to compute and |
| // verify MACs. |
| type wrappedMAC struct { |
| ps *primitiveset.PrimitiveSet |
| } |
| |
| func newWrappedMAC(ps *primitiveset.PrimitiveSet) (*wrappedMAC, error) { |
| if _, ok := (ps.Primary.Primitive).(tink.MAC); !ok { |
| return nil, fmt.Errorf("mac_factory: not a MAC primitive") |
| } |
| |
| for _, primitives := range ps.Entries { |
| for _, p := range primitives { |
| if _, ok := (p.Primitive).(tink.MAC); !ok { |
| return nil, fmt.Errorf("mac_factory: not an MAC primitive") |
| } |
| } |
| } |
| |
| ret := new(wrappedMAC) |
| ret.ps = ps |
| |
| return ret, nil |
| } |
| |
| // ComputeMAC calculates a MAC over the given data using the primary primitive |
| // and returns the concatenation of the primary's identifier and the calculated mac. |
| func (m *wrappedMAC) ComputeMAC(data []byte) ([]byte, error) { |
| primary := m.ps.Primary |
| primitive, ok := (primary.Primitive).(tink.MAC) |
| if !ok { |
| return nil, fmt.Errorf("mac_factory: not a MAC primitive") |
| } |
| if m.ps.Primary.PrefixType == tinkpb.OutputPrefixType_LEGACY { |
| d := data |
| data = make([]byte, 0, len(d)+1) |
| data = append(data, d...) |
| data = append(data, byte(0)) |
| } |
| mac, err := primitive.ComputeMAC(data) |
| if err != nil { |
| return nil, err |
| } |
| return append([]byte(primary.Prefix), mac...), nil |
| } |
| |
| var errInvalidMAC = fmt.Errorf("mac_factory: invalid mac") |
| |
| // VerifyMAC verifies whether the given mac is a correct authentication code |
| // for the given data. |
| func (m *wrappedMAC) VerifyMAC(mac, data []byte) error { |
| // This also rejects raw MAC with size of 4 bytes or fewer. Those MACs are |
| // clearly insecure, thus should be discouraged. |
| prefixSize := cryptofmt.NonRawPrefixSize |
| if len(mac) <= prefixSize { |
| return errInvalidMAC |
| } |
| |
| // try non raw keys |
| prefix := mac[:prefixSize] |
| macNoPrefix := mac[prefixSize:] |
| entries, err := m.ps.EntriesForPrefix(string(prefix)) |
| if err == nil { |
| for i := 0; i < len(entries); i++ { |
| entry := entries[i] |
| p, ok := (entry.Primitive).(tink.MAC) |
| if !ok { |
| return fmt.Errorf("mac_factory: not an MAC primitive") |
| } |
| if entry.PrefixType == tinkpb.OutputPrefixType_LEGACY { |
| d := data |
| data = make([]byte, 0, len(d)+1) |
| data = append(data, d...) |
| data = append(data, byte(0)) |
| } |
| if err = p.VerifyMAC(macNoPrefix, data); err == nil { |
| return nil |
| } |
| } |
| } |
| |
| // try raw keys |
| entries, err = m.ps.RawEntries() |
| if err == nil { |
| for i := 0; i < len(entries); i++ { |
| p, ok := (entries[i].Primitive).(tink.MAC) |
| if !ok { |
| return fmt.Errorf("mac_factory: not an MAC primitive") |
| } |
| |
| if err = p.VerifyMAC(mac, data); err == nil { |
| return nil |
| } |
| } |
| } |
| |
| // nothing worked |
| return errInvalidMAC |
| } |