// Calculate signature.
	newSignature := getSignature(signingKey, stringToSign)

	// Verify if signature match.
	if !compareSignatureV4(newSignature, signV4Values.Signature) {
		return cred, "", "", time.Time{}, ErrSignatureDoesNotMatch
	}

	// Return calculated signature.
	return cred, newSignature, region, date, ErrNone
}

	// Get signing key.
	signingKey := getSigningKey(cred.SecretKey, credHeader.scope.date, credHeader.scope.region, serviceS3)

	// Get signature.
	newSignature := getSignature(signingKey, formValues.Get("Policy"))

	// Verify signature.
	if !compareSignatureV4(newSignature, formValues.Get(xhttp.AmzSignature)) {
		return cred, ErrSignatureDoesNotMatch
	}

	// Success.
	return cred, ErrNone
}

pkg go/token, const TILDE = 88
pkg go/token, const TILDE Token
pkg go/types, func Instantiate(*Context, Type, []Type, bool) (Type, error)
pkg go/types, func NewContext() *Context
pkg go/types, func NewSignature //deprecated
pkg go/types, func NewSignatureType(*Var, []*TypeParam, []*TypeParam, *Tuple, *Tuple, bool) *Signature
pkg go/types, func NewTerm(bool, Type) *Term
pkg go/types, func NewTypeParam(*TypeName, Type) *TypeParam