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Add support for signing with Tink keyset (#2228)
This allows deployers to securely sign in-memory while mitigating key exfiltration, since the key is encrypted at rest and loaded into memory at server startup. Requires providing a path to an encrypted Tink keyset and the Key Encryption Key, a KMS URI for decrypting the keyset. Heavily pulls from Fulcio's Tink implementation. Signed-off-by: Hayden Blauzvern <[email protected]>
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,87 @@ | ||
| // Copyright 2024 The Sigstore Authors. | ||
| // | ||
| // 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 signer | ||
|
|
||
| import ( | ||
| "context" | ||
| "errors" | ||
| "os" | ||
| "path/filepath" | ||
| "strings" | ||
|
|
||
| tinkUtils "github.com/sigstore/rekor/pkg/signer/tink" | ||
| "github.com/tink-crypto/tink-go-awskms/v2/integration/awskms" | ||
| "github.com/tink-crypto/tink-go-gcpkms/v2/integration/gcpkms" | ||
| "github.com/tink-crypto/tink-go/v2/core/registry" | ||
| "github.com/tink-crypto/tink-go/v2/keyset" | ||
| "github.com/tink-crypto/tink-go/v2/tink" | ||
|
|
||
| "github.com/sigstore/sigstore/pkg/signature" | ||
| ) | ||
|
|
||
| const TinkScheme = "tink" | ||
|
|
||
| // NewTinkSignerWithHandle returns a signature.SignerVerifier that wraps crypto.Signer and a hash function. | ||
| // Provide a path to the encrypted keyset and cloud KMS key URI for decryption | ||
| func NewTinkSigner(ctx context.Context, kekURI, keysetPath string) (signature.Signer, error) { | ||
| kek, err := getKeyEncryptionKey(ctx, kekURI) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
| return NewTinkSignerWithHandle(kek, keysetPath) | ||
| } | ||
|
|
||
| // NewTinkSignerWithHandle returns a signature.SignerVerifier that wraps crypto.Signer and a hash function. | ||
| // Provide a path to the encrypted keyset and a key handle for decrypting the keyset | ||
| func NewTinkSignerWithHandle(kek tink.AEAD, keysetPath string) (signature.Signer, error) { | ||
| f, err := os.Open(filepath.Clean(keysetPath)) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
| defer f.Close() | ||
|
|
||
| kh, err := keyset.Read(keyset.NewJSONReader(f), kek) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
| signer, hash, err := tinkUtils.KeyHandleToSigner(kh) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
| return signature.LoadSignerVerifier(signer, hash) | ||
| } | ||
|
|
||
| // getKeyEncryptionKey returns a Tink AEAD encryption key from KMS | ||
| // Supports GCP and AWS | ||
| func getKeyEncryptionKey(ctx context.Context, kmsKey string) (tink.AEAD, error) { | ||
| switch { | ||
| case strings.HasPrefix(kmsKey, "gcp-kms://"): | ||
| gcpClient, err := gcpkms.NewClientWithOptions(ctx, kmsKey) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
| registry.RegisterKMSClient(gcpClient) | ||
| return gcpClient.GetAEAD(kmsKey) | ||
| case strings.HasPrefix(kmsKey, "aws-kms://"): | ||
| awsClient, err := awskms.NewClientWithOptions(kmsKey) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
| registry.RegisterKMSClient(awsClient) | ||
| return awsClient.GetAEAD(kmsKey) | ||
| default: | ||
| return nil, errors.New("unsupported KMS key type") | ||
| } | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,157 @@ | ||
| // Copyright 2024 The Sigstore Authors. | ||
| // | ||
| // 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 tink | ||
|
|
||
| // Copy of https://github.com/sigstore/fulcio/blob/a781da9903c63a2cd2c0f0c1c2bfc763196db44f/pkg/ca/tinkca/signer.go | ||
| // with a modification for including the hash function when creating the signer | ||
|
|
||
| import ( | ||
| "crypto" | ||
| "crypto/ecdsa" | ||
| "crypto/ed25519" | ||
| "errors" | ||
| "fmt" | ||
| "math/big" | ||
|
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| "github.com/tink-crypto/tink-go/v2/insecurecleartextkeyset" | ||
| "github.com/tink-crypto/tink-go/v2/keyset" | ||
| commonpb "github.com/tink-crypto/tink-go/v2/proto/common_go_proto" | ||
| ecdsapb "github.com/tink-crypto/tink-go/v2/proto/ecdsa_go_proto" | ||
| ed25519pb "github.com/tink-crypto/tink-go/v2/proto/ed25519_go_proto" | ||
| tinkpb "github.com/tink-crypto/tink-go/v2/proto/tink_go_proto" | ||
| signatureSubtle "github.com/tink-crypto/tink-go/v2/signature/subtle" | ||
| "github.com/tink-crypto/tink-go/v2/subtle" | ||
| "google.golang.org/protobuf/proto" | ||
| ) | ||
|
|
||
| var ( | ||
| ecdsaSignerKeyVersion = 0 | ||
| ecdsaSignerTypeURL = "type.googleapis.com/google.crypto.tink.EcdsaPrivateKey" | ||
| ed25519SignerKeyVersion = 0 | ||
| ed25519SignerTypeURL = "type.googleapis.com/google.crypto.tink.Ed25519PrivateKey" | ||
| ) | ||
|
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| // KeyHandleToSigner converts a key handle to the crypto.Signer interface. | ||
| // Heavily pulls from Tink's signature and subtle packages. | ||
| func KeyHandleToSigner(kh *keyset.Handle) (crypto.Signer, crypto.Hash, error) { | ||
| // extract the key material from the key handle | ||
| ks := insecurecleartextkeyset.KeysetMaterial(kh) | ||
|
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| k := getPrimaryKey(ks) | ||
| if k == nil { | ||
| return nil, 0, errors.New("no enabled key found in keyset") | ||
| } | ||
|
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| switch k.GetTypeUrl() { | ||
| case ecdsaSignerTypeURL: | ||
| // https://github.com/tink-crypto/tink-go/blob/0aadc94a816408c4bdf95885b3c9860ecfd55fc0/signature/ecdsa/signer_key_manager.go#L48 | ||
| privKey := new(ecdsapb.EcdsaPrivateKey) | ||
| if err := proto.Unmarshal(k.GetValue(), privKey); err != nil { | ||
| return nil, 0, fmt.Errorf("error unmarshalling ecdsa private key: %w", err) | ||
| } | ||
| if err := validateEcdsaPrivKey(privKey); err != nil { | ||
| return nil, 0, fmt.Errorf("error validating ecdsa private key: %w", err) | ||
| } | ||
| // https://github.com/tink-crypto/tink-go/blob/0aadc94a816408c4bdf95885b3c9860ecfd55fc0/signature/subtle/ecdsa_signer.go#L37 | ||
| hashAlg, curve, _ := getECDSAParamNames(privKey.PublicKey.Params) | ||
| p := new(ecdsa.PrivateKey) | ||
| c := subtle.GetCurve(curve) | ||
| if c == nil { | ||
| return nil, 0, errors.New("tink ecdsa signer: invalid curve") | ||
| } | ||
| p.PublicKey.Curve = c | ||
| p.D = new(big.Int).SetBytes(privKey.GetKeyValue()) | ||
| p.PublicKey.X, p.PublicKey.Y = c.ScalarBaseMult(privKey.GetKeyValue()) | ||
| hash := getHashFunc(hashAlg) | ||
| return p, hash, nil | ||
| case ed25519SignerTypeURL: | ||
| // https://github.com/tink-crypto/tink-go/blob/0aadc94a816408c4bdf95885b3c9860ecfd55fc0/signature/ed25519/signer_key_manager.go#L47 | ||
| privKey := new(ed25519pb.Ed25519PrivateKey) | ||
| if err := proto.Unmarshal(k.GetValue(), privKey); err != nil { | ||
| return nil, 0, fmt.Errorf("error unmarshalling ed25519 private key: %w", err) | ||
| } | ||
| if err := validateEd25519PrivKey(privKey); err != nil { | ||
| return nil, 0, fmt.Errorf("error validating ed25519 private key: %w", err) | ||
| } | ||
| // https://github.com/tink-crypto/tink-go/blob/0aadc94a816408c4bdf95885b3c9860ecfd55fc0/signature/subtle/ed25519_signer.go#L27 | ||
| p := ed25519.NewKeyFromSeed(privKey.GetKeyValue()) | ||
| return p, crypto.SHA512, nil | ||
| default: | ||
| return nil, 0, fmt.Errorf("unsupported key type: %s", k.GetTypeUrl()) | ||
| } | ||
| } | ||
|
|
||
| // getPrimaryKey returns the first enabled key from a keyset. | ||
| func getPrimaryKey(ks *tinkpb.Keyset) *tinkpb.KeyData { | ||
| for _, k := range ks.GetKey() { | ||
| if k.GetKeyId() == ks.GetPrimaryKeyId() && k.GetStatus() == tinkpb.KeyStatusType_ENABLED { | ||
| return k.GetKeyData() | ||
| } | ||
| } | ||
| return nil | ||
| } | ||
|
|
||
| // validateEcdsaPrivKey validates the given ECDSAPrivateKey. | ||
| // https://github.com/tink-crypto/tink-go/blob/0aadc94a816408c4bdf95885b3c9860ecfd55fc0/signature/ecdsa/signer_key_manager.go#L151 | ||
| func validateEcdsaPrivKey(key *ecdsapb.EcdsaPrivateKey) error { | ||
| if err := keyset.ValidateKeyVersion(key.Version, uint32(ecdsaSignerKeyVersion)); err != nil { | ||
| return fmt.Errorf("ecdsa: invalid key version in key: %s", err) | ||
| } | ||
| if err := keyset.ValidateKeyVersion(key.GetPublicKey().GetVersion(), uint32(ecdsaSignerKeyVersion)); err != nil { | ||
| return fmt.Errorf("ecdsa: invalid public version in key: %s", err) | ||
| } | ||
| hash, curve, encoding := getECDSAParamNames(key.PublicKey.Params) | ||
| return signatureSubtle.ValidateECDSAParams(hash, curve, encoding) | ||
| } | ||
|
|
||
| // getECDSAParamNames returns the string representations of each parameter in | ||
| // the given ECDSAParams. | ||
| // https://github.com/tink-crypto/tink-go/blob/0aadc94a816408c4bdf95885b3c9860ecfd55fc0/signature/ecdsa/proto.go#L24 | ||
| func getECDSAParamNames(params *ecdsapb.EcdsaParams) (string, string, string) { | ||
| hashName := commonpb.HashType_name[int32(params.GetHashType())] | ||
| curveName := commonpb.EllipticCurveType_name[int32(params.GetCurve())] | ||
| encodingName := ecdsapb.EcdsaSignatureEncoding_name[int32(params.GetEncoding())] | ||
| return hashName, curveName, encodingName | ||
| } | ||
|
|
||
| // validateEd25519PrivKey validates the given ED25519PrivateKey. | ||
| // https://github.com/tink-crypto/tink-go/blob/0aadc94a816408c4bdf95885b3c9860ecfd55fc0/signature/ed25519/signer_key_manager.go#L157 | ||
| func validateEd25519PrivKey(key *ed25519pb.Ed25519PrivateKey) error { | ||
| if err := keyset.ValidateKeyVersion(key.Version, uint32(ed25519SignerKeyVersion)); err != nil { | ||
| return fmt.Errorf("ed25519: invalid key: %w", err) | ||
| } | ||
| if len(key.KeyValue) != ed25519.SeedSize { | ||
| return fmt.Errorf("ed25519: invalid key length, got %d", len(key.KeyValue)) | ||
| } | ||
| return nil | ||
| } | ||
|
|
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| // getHashFunc returns the hash function for a given hash name | ||
| func getHashFunc(hash string) crypto.Hash { | ||
| switch hash { | ||
| case "SHA1": | ||
| return crypto.SHA1 | ||
| case "SHA224": | ||
| return crypto.SHA224 | ||
| case "SHA256": | ||
| return crypto.SHA256 | ||
| case "SHA384": | ||
| return crypto.SHA384 | ||
| case "SHA512": | ||
| return crypto.SHA512 | ||
| default: | ||
| return crypto.SHA256 | ||
| } | ||
| } |
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