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package sasquatch
import (
"crypto/hmac"
"crypto/sha256"
"io"
"golang.org/x/crypto/chacha20poly1305"
"golang.org/x/crypto/hkdf"
)
func aeadEncrypt(key, plaintext []byte) ([]byte, error) {
aead, err := chacha20poly1305.New(key)
if err != nil {
return nil, err
}
nonce := make([]byte, chacha20poly1305.NonceSize)
return aead.Seal(nil, nonce, plaintext, nil), nil
}
func aeadDecrypt(key, ciphertext []byte) ([]byte, error) {
aead, err := chacha20poly1305.New(key)
if err != nil {
return nil, err
}
nonce := make([]byte, chacha20poly1305.NonceSize)
return aead.Open(nil, nonce, ciphertext, nil)
}
func headerMAC(fileKey []byte, hdr *Header) ([]byte, error) {
h := hkdf.New(sha256.New, fileKey, nil, []byte("header"))
hmacKey := make([]byte, 32)
if _, err := io.ReadFull(h, hmacKey); err != nil {
return nil, err
}
hh := hmac.New(sha256.New, hmacKey)
if err := hdr.MarshalWithoutMAC(hh); err != nil {
return nil, err
}
return hh.Sum(nil), nil
}
func streamKey(fileKey, nonce []byte) []byte {
h := hkdf.New(sha256.New, fileKey, nonce, []byte("payload"))
streamKey := make([]byte, chacha20poly1305.KeySize)
if _, err := io.ReadFull(h, streamKey); err != nil {
panic("internal error: failed to read from HKDF: " + err.Error())
}
return streamKey
}
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