crypto

Documentation

Overview

Package crypto provides cryptographic primitives for cryptkey: HKDF-SHA256 key derivation and AES-256-GCM authenticated encryption of Shamir shares.

Index

• func ConfigHMAC(masterKey, data []byte) ([]byte, error)
• func DecryptShare(providerSecret, aad []byte, es *EncryptedShare) ([]byte, error)
• func DeriveOutputKey(masterKey, salt []byte, info string, length int) ([]byte, error)
• func VerifyConfigHMAC(masterKey, data, expected []byte) (bool, error)
• func WipeBytes(b []byte)
• type EncryptedShare
  • func EncryptShare(providerSecret, share, aad []byte) (*EncryptedShare, error)

Functions

func ConfigHMAC

func ConfigHMAC(masterKey, data []byte) ([]byte, error)

ConfigHMAC computes an HMAC-SHA256 over data using a key derived from the master key. Used to detect config tampering without storing the master key.

func DecryptShare

func DecryptShare(providerSecret, aad []byte, es *EncryptedShare) ([]byte, error)

DecryptShare decrypts a Shamir share using a provider's 32-byte secret. The aad must match the value used during encryption.

func DeriveOutputKey

func DeriveOutputKey(masterKey, salt []byte, info string, length int) ([]byte, error)

DeriveOutputKey stretches a reconstructed master key through HKDF-SHA256 into a final output key of the requested length. salt and info provide per-profile domain separation.

func VerifyConfigHMAC

func VerifyConfigHMAC(masterKey, data, expected []byte) (bool, error)

VerifyConfigHMAC checks a config HMAC against expected.

func WipeBytes

func WipeBytes(b []byte)

WipeBytes zeroes a byte slice and uses runtime.KeepAlive to discourage the compiler from optimizing the zeroing away. This is a best-effort mitigation: Go's garbage collector may copy heap objects during compaction, leaving prior copies in freed pages that are not wiped. For true memory-forensic resistance, an mlock/madvise approach or a non-GC language would be required. Use this for all secret material cleanup regardless — it raises the bar meaningfully.

Types

type EncryptedShare

type EncryptedShare struct {
	Ciphertext []byte // AES-256-GCM ciphertext (includes GCM tag)
	Nonce      []byte // GCM nonce
	Salt       []byte // HKDF salt used to derive the AES key
}

EncryptedShare holds the ciphertext and parameters needed to decrypt a Shamir share given the originating provider's 32-byte secret.

func EncryptShare

func EncryptShare(providerSecret, share, aad []byte) (*EncryptedShare, error)

EncryptShare encrypts a Shamir share using a provider's 32-byte secret. The aad parameter binds the ciphertext to context (e.g. provider type and ID).

Flow: HKDF-SHA256(secret, random_salt, info) → 32-byte AES key → AES-256-GCM(share, aad).