sha := sha256.New()
		sha.Write(extKey)
		sha.Write(sealedKey.IV[:])
		unsealConfig = sio.Config{MinVersion: sio.Version10, Key: sha.Sum(nil), CipherSuites: fips.DARECiphers()}
	}

	if out, err := sio.DecryptBuffer(key[:0], sealedKey.Key[:], unsealConfig); len(out) != 32 || err != nil {
		return ErrSecretKeyMismatch
	}
	return nil
}

// DerivePartKey derives an unique 256 bit key from an ObjectKey and the part index.

	if !etag.IsEncrypted() {
		return etag, nil
	}
	mac := hmac.New(sha256.New, key)
	mac.Write([]byte(HMACContext))
	decryptionKey := mac.Sum(nil)

	plaintext := make([]byte, 0, 16)
	etag, err := sio.DecryptBuffer(plaintext, etag, sio.Config{
		Key:          decryptionKey,
		CipherSuites: fips.DARECiphers(),
	})
	if err != nil {
		return nil, err
	}
	return etag, nil
}

		}
		key, err := decryptObjectMeta(key, o.Bucket, o.Name, o.UserDefined)
		if err != nil {
			return nil, err
		}
		mac := hmac.New(sha256.New, key)
		mac.Write([]byte(baseKey))
		return sio.DecryptBuffer(nil, input, sio.Config{Key: mac.Sum(nil), CipherSuites: fips.DARECiphers()})
	}
}

// decryptChecksums will attempt to decode checksums and return it/them if set.