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// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package crypto collects common cryptographic constants.
package crypto
import (
// Hash identifies a cryptographic hash function that is implemented in another
// package.
type Hash uint
// HashFunc simply returns the value of h so that Hash implements SignerOpts.
func (h Hash) HashFunc() Hash {
return h
const (
MD4 Hash = 1 + iota // import
MD5 // import crypto/md5
SHA1 // import crypto/sha1
SHA224 // import crypto/sha256
SHA256 // import crypto/sha256
SHA384 // import crypto/sha512
SHA512 // import crypto/sha512
MD5SHA1 // no implementation; MD5+SHA1 used for TLS RSA
RIPEMD160 // import
SHA3_224 // import
SHA3_256 // import
SHA3_384 // import
SHA3_512 // import
var digestSizes = []uint8{
MD4: 16,
MD5: 16,
SHA1: 20,
SHA224: 28,
SHA256: 32,
SHA384: 48,
SHA512: 64,
SHA3_224: 28,
SHA3_256: 32,
SHA3_384: 48,
SHA3_512: 64,
MD5SHA1: 36,
RIPEMD160: 20,
// Size returns the length, in bytes, of a digest resulting from the given hash
// function. It doesn't require that the hash function in question be linked
// into the program.
func (h Hash) Size() int {
if h > 0 && h < maxHash {
return int(digestSizes[h])
panic("crypto: Size of unknown hash function")
var hashes = make([]func() hash.Hash, maxHash)
// New returns a new hash.Hash calculating the given hash function. New panics
// if the hash function is not linked into the binary.
func (h Hash) New() hash.Hash {
if h > 0 && h < maxHash {
f := hashes[h]
if f != nil {
return f()
panic("crypto: requested hash function #" + strconv.Itoa(int(h)) + " is unavailable")
// Available reports whether the given hash function is linked into the binary.
func (h Hash) Available() bool {
return h < maxHash && hashes[h] != nil
// RegisterHash registers a function that returns a new instance of the given
// hash function. This is intended to be called from the init function in
// packages that implement hash functions.
func RegisterHash(h Hash, f func() hash.Hash) {
if h >= maxHash {
panic("crypto: RegisterHash of unknown hash function")
hashes[h] = f
// PublicKey represents a public key using an unspecified algorithm.
type PublicKey interface{}
// PrivateKey represents a private key using an unspecified algorithm.
type PrivateKey interface{}
// Signer is an interface for an opaque private key that can be used for
// signing operations. For example, an RSA key kept in a hardware module.
type Signer interface {
// Public returns the public key corresponding to the opaque,
// private key.
Public() PublicKey
// Sign signs msg with the private key, possibly using entropy from
// rand. For an RSA key, the resulting signature should be either a
// PKCS#1 v1.5 or PSS signature (as indicated by opts). For an (EC)DSA
// key, it should be a DER-serialised, ASN.1 signature structure.
// Hash implements the SignerOpts interface and, in most cases, one can
// simply pass in the hash function used as opts. Sign may also attempt
// to type assert opts to other types in order to obtain algorithm
// specific values. See the documentation in each package for details.
Sign(rand io.Reader, msg []byte, opts SignerOpts) (signature []byte, err error)
// SignerOpts contains options for signing with a Signer.
type SignerOpts interface {
// HashFunc returns an identifier for the hash function used to produce
// the message passed to Signer.Sign, or else zero to indicate that no
// hashing was done.
HashFunc() Hash