Kyle Isom
115f23a3ea
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>
63 lines
1.7 KiB
Go
63 lines
1.7 KiB
Go
package tpm2
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import (
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"crypto/aes"
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"crypto/cipher"
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"crypto/hmac"
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"errors"
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"fmt"
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)
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var (
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labelStorage = "STORAGE"
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labelIntegrity = "INTEGRITY"
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ErrUnsupportedCipher = errors.New("unsupported block cipher")
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ErrUnsupportedMode = errors.New("unsupported block cipher mode of operation")
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)
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// deriveAndEncrypt derives a symmetric key and uses it to encrypt the plaintext.
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func deriveAndEncrypt(pub LabeledEncapsulationKey, seed []byte, context []byte, plaintext []byte) ([]byte, error) {
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// Only AES is supported.
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if pub.SymmetricParameters().Algorithm != TPMAlgAES {
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return nil, fmt.Errorf("%w %v", ErrUnsupportedCipher, pub.SymmetricParameters().Algorithm)
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}
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mode, err := pub.SymmetricParameters().Mode.AES()
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if err != nil {
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return nil, err
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}
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if *mode != TPMAlgCFB {
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return nil, fmt.Errorf("%w %v", ErrUnsupportedMode, *mode)
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}
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bits, err := pub.SymmetricParameters().KeyBits.AES()
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if err != nil {
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return nil, err
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}
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hash, err := pub.NameAlg().Hash()
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if err != nil {
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return nil, err
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}
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key, err := aes.NewCipher(KDFa(hash, seed, labelStorage, context, nil, int(*bits)))
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if err != nil {
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return nil, err
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}
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ciphertext := make([]byte, len(plaintext))
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cipher.NewCFBEncrypter(key, make([]byte, key.BlockSize())).XORKeyStream(ciphertext, plaintext)
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return ciphertext, nil
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}
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// deriveAndHMAC derives an HMAC key and uses it to HMAC the data, which can be provided in multiple chunks.
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func deriveAndHMAC(pub LabeledEncapsulationKey, seed []byte, data ...[]byte) ([]byte, error) {
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hash, err := pub.NameAlg().Hash()
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if err != nil {
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return nil, err
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}
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key := KDFa(hash, seed, labelIntegrity, nil, nil, hash.Size()*8)
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hmac := hmac.New(hash.New, key)
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for _, data := range data {
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hmac.Write(data)
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}
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return hmac.Sum(nil), nil
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}
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