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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"
)

// Hash identifies a cryptographic hash function that is implemented in another
// package.
type Hash uint

const (
        MD4       Hash = 1 + iota // import code.google.com/p/go.crypto/md4
        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 code.google.com/p/go.crypto/ripemd160
        maxHash
)

var digestSizes = []uint8{
        MD4:       16,
        MD5:       16,
        SHA1:      20,
        SHA224:    28,
        SHA256:    32,
        SHA384:    48,
        SHA512:    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 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
}

// PrivateKey represents a private key using an unspecified algorithm.
type PrivateKey interface{}