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package spectre

import (
	"crypto/hmac"
	"crypto/sha256"
)

func siteKey(userKey []byte, scoper Scoper, siteName string, counter int, scope Scope) []byte {
	nameBytes := []byte(siteName)
	scopeBytes := []byte(scoper.Scope(scope))

	nameBytesLen := len(nameBytes)
	keySalt := append(scopeBytes,
		byte(nameBytesLen>>24),
		byte(nameBytesLen>>16),
		byte(nameBytesLen>>8),
		byte(nameBytesLen),
	)
	keySalt = append(keySalt, nameBytes...)
	keySalt = append(keySalt,
		byte(counter>>24),
		byte(counter>>16),
		byte(counter>>8),
		byte(counter),
	)

	sign := hmac.New(sha256.New, userKey)
	sign.Write(keySalt)

	return sign.Sum(nil)
}