| package rfc4757 |
| |
| import ( |
| "bytes" |
| "encoding/hex" |
| "errors" |
| "fmt" |
| "io" |
| |
| "golang.org/x/crypto/md4" |
| ) |
| |
| // StringToKey returns a key derived from the string provided according to the definition in RFC 4757. |
| func StringToKey(secret string) ([]byte, error) { |
| b := make([]byte, len(secret)*2, len(secret)*2) |
| for i, r := range secret { |
| u := fmt.Sprintf("%04x", r) |
| c, err := hex.DecodeString(u) |
| if err != nil { |
| return []byte{}, errors.New("character could not be encoded") |
| } |
| // Swap round the two bytes to make little endian as we put into byte slice |
| b[2*i] = c[1] |
| b[2*i+1] = c[0] |
| } |
| r := bytes.NewReader(b) |
| h := md4.New() |
| _, err := io.Copy(h, r) |
| if err != nil { |
| return []byte{}, err |
| } |
| return h.Sum(nil), nil |
| } |
| |
| func deriveKeys(key, checksum []byte, usage uint32, export bool) (k1, k2, k3 []byte) { |
| k1 = key |
| k2 = HMAC(k1, UsageToMSMsgType(usage)) |
| k3 = HMAC(k2, checksum) |
| return |
| } |