Add Nix flake for mciasctl and mciasgrpcctl

Vendor dependencies and expose control program binaries via
nix build. Uses nixpkgs-unstable for Go 1.26 support.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

vendor/github.com/google/go-tpm/tpm2/child_object_crypto.go

@@ -0,0 +1,62 @@
+package tpm2
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/hmac"
+	"errors"
+	"fmt"
+)
+
+var (
+	labelStorage   = "STORAGE"
+	labelIntegrity = "INTEGRITY"
+
+	ErrUnsupportedCipher = errors.New("unsupported block cipher")
+	ErrUnsupportedMode   = errors.New("unsupported block cipher mode of operation")
+)
+
+// deriveAndEncrypt derives a symmetric key and uses it to encrypt the plaintext.
+func deriveAndEncrypt(pub LabeledEncapsulationKey, seed []byte, context []byte, plaintext []byte) ([]byte, error) {
+	// Only AES is supported.
+	if pub.SymmetricParameters().Algorithm != TPMAlgAES {
+		return nil, fmt.Errorf("%w %v", ErrUnsupportedCipher, pub.SymmetricParameters().Algorithm)
+	}
+	mode, err := pub.SymmetricParameters().Mode.AES()
+	if err != nil {
+		return nil, err
+	}
+	if *mode != TPMAlgCFB {
+		return nil, fmt.Errorf("%w %v", ErrUnsupportedMode, *mode)
+	}
+	bits, err := pub.SymmetricParameters().KeyBits.AES()
+	if err != nil {
+		return nil, err
+	}
+
+	hash, err := pub.NameAlg().Hash()
+	if err != nil {
+		return nil, err
+	}
+	key, err := aes.NewCipher(KDFa(hash, seed, labelStorage, context, nil, int(*bits)))
+	if err != nil {
+		return nil, err
+	}
+	ciphertext := make([]byte, len(plaintext))
+	cipher.NewCFBEncrypter(key, make([]byte, key.BlockSize())).XORKeyStream(ciphertext, plaintext)
+	return ciphertext, nil
+}
+
+// deriveAndHMAC derives an HMAC key and uses it to HMAC the data, which can be provided in multiple chunks.
+func deriveAndHMAC(pub LabeledEncapsulationKey, seed []byte, data ...[]byte) ([]byte, error) {
+	hash, err := pub.NameAlg().Hash()
+	if err != nil {
+		return nil, err
+	}
+	key := KDFa(hash, seed, labelIntegrity, nil, nil, hash.Size()*8)
+	hmac := hmac.New(hash.New, key)
+	for _, data := range data {
+		hmac.Write(data)
+	}
+	return hmac.Sum(nil), nil
+}