mirror of
https://github.com/cheat/cheat.git
synced 2024-09-08 20:51:34 +02:00
Integrate `go-git` into the application, and use it to `git clone` cheatsheets when the installer runs. Previously, the installer required that `git` be installed on the system `PATH`, so this change has to big advantages: 1. It removes that system dependency on `git` 2. It paves the way for implementing the `--update` command Additionally, `cheat` now performs a `--depth=1` clone when installing cheatsheets, which should at least somewhat improve installation times (especially on slow network connections).
454 lines
14 KiB
Go
454 lines
14 KiB
Go
// Package ed25519 implements Ed25519 signature scheme as described in RFC-8032.
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//
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// This package provides optimized implementations of the three signature
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// variants and maintaining closer compatiblilty with crypto/ed25519.
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//
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// | Scheme Name | Sign Function | Verification | Context |
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// |-------------|-------------------|---------------|-------------------|
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// | Ed25519 | Sign | Verify | None |
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// | Ed25519Ph | SignPh | VerifyPh | Yes, can be empty |
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// | Ed25519Ctx | SignWithCtx | VerifyWithCtx | Yes, non-empty |
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// | All above | (PrivateKey).Sign | VerifyAny | As above |
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//
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// Specific functions for sign and verify are defined. A generic signing
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// function for all schemes is available through the crypto.Signer interface,
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// which is implemented by the PrivateKey type. A correspond all-in-one
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// verification method is provided by the VerifyAny function.
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//
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// Signing with Ed25519Ph or Ed25519Ctx requires a context string for domain
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// separation. This parameter is passed using a SignerOptions struct defined
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// in this package. While Ed25519Ph accepts an empty context, Ed25519Ctx
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// enforces non-empty context strings.
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//
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// Compatibility with crypto.ed25519
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//
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// These functions are compatible with the “Ed25519” function defined in
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// RFC-8032. However, unlike RFC 8032's formulation, this package's private
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// key representation includes a public key suffix to make multiple signing
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// operations with the same key more efficient. This package refers to the
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// RFC-8032 private key as the “seed”.
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//
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// References
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//
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// - RFC-8032: https://rfc-editor.org/rfc/rfc8032.txt
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// - Ed25519: https://ed25519.cr.yp.to/
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// - EdDSA: High-speed high-security signatures. https://doi.org/10.1007/s13389-012-0027-1
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package ed25519
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import (
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"bytes"
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"crypto"
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cryptoRand "crypto/rand"
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"crypto/sha512"
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"crypto/subtle"
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"errors"
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"fmt"
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"io"
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"strconv"
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"github.com/cloudflare/circl/sign"
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)
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const (
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// ContextMaxSize is the maximum length (in bytes) allowed for context.
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ContextMaxSize = 255
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// PublicKeySize is the size, in bytes, of public keys as used in this package.
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PublicKeySize = 32
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// PrivateKeySize is the size, in bytes, of private keys as used in this package.
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PrivateKeySize = 64
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// SignatureSize is the size, in bytes, of signatures generated and verified by this package.
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SignatureSize = 64
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// SeedSize is the size, in bytes, of private key seeds. These are the private key representations used by RFC 8032.
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SeedSize = 32
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)
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const (
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paramB = 256 / 8 // Size of keys in bytes.
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)
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// SignerOptions implements crypto.SignerOpts and augments with parameters
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// that are specific to the Ed25519 signature schemes.
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type SignerOptions struct {
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// Hash must be crypto.Hash(0) for Ed25519/Ed25519ctx, or crypto.SHA512
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// for Ed25519ph.
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crypto.Hash
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// Context is an optional domain separation string for Ed25519ph and a
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// must for Ed25519ctx. Its length must be less or equal than 255 bytes.
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Context string
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// Scheme is an identifier for choosing a signature scheme. The zero value
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// is ED25519.
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Scheme SchemeID
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}
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// SchemeID is an identifier for each signature scheme.
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type SchemeID uint
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const (
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ED25519 SchemeID = iota
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ED25519Ph
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ED25519Ctx
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)
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// PrivateKey is the type of Ed25519 private keys. It implements crypto.Signer.
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type PrivateKey []byte
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// Equal reports whether priv and x have the same value.
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func (priv PrivateKey) Equal(x crypto.PrivateKey) bool {
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xx, ok := x.(PrivateKey)
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return ok && subtle.ConstantTimeCompare(priv, xx) == 1
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}
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// Public returns the PublicKey corresponding to priv.
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func (priv PrivateKey) Public() crypto.PublicKey {
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publicKey := make(PublicKey, PublicKeySize)
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copy(publicKey, priv[SeedSize:])
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return publicKey
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}
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// Seed returns the private key seed corresponding to priv. It is provided for
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// interoperability with RFC 8032. RFC 8032's private keys correspond to seeds
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// in this package.
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func (priv PrivateKey) Seed() []byte {
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seed := make([]byte, SeedSize)
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copy(seed, priv[:SeedSize])
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return seed
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}
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func (priv PrivateKey) Scheme() sign.Scheme { return sch }
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func (pub PublicKey) Scheme() sign.Scheme { return sch }
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func (priv PrivateKey) MarshalBinary() (data []byte, err error) {
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privateKey := make(PrivateKey, PrivateKeySize)
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copy(privateKey, priv)
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return privateKey, nil
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}
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func (pub PublicKey) MarshalBinary() (data []byte, err error) {
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publicKey := make(PublicKey, PublicKeySize)
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copy(publicKey, pub)
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return publicKey, nil
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}
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// Equal reports whether pub and x have the same value.
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func (pub PublicKey) Equal(x crypto.PublicKey) bool {
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xx, ok := x.(PublicKey)
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return ok && bytes.Equal(pub, xx)
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}
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// Sign creates a signature of a message with priv key.
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// This function is compatible with crypto.ed25519 and also supports the
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// three signature variants defined in RFC-8032, namely Ed25519 (or pure
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// EdDSA), Ed25519Ph, and Ed25519Ctx.
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// The opts.HashFunc() must return zero to specify either Ed25519 or Ed25519Ctx
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// variant. This can be achieved by passing crypto.Hash(0) as the value for
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// opts.
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// The opts.HashFunc() must return SHA512 to specify the Ed25519Ph variant.
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// This can be achieved by passing crypto.SHA512 as the value for opts.
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// Use a SignerOptions struct (defined in this package) to pass a context
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// string for signing.
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func (priv PrivateKey) Sign(
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rand io.Reader,
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message []byte,
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opts crypto.SignerOpts,
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) (signature []byte, err error) {
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var ctx string
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var scheme SchemeID
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if o, ok := opts.(SignerOptions); ok {
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ctx = o.Context
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scheme = o.Scheme
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}
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switch true {
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case scheme == ED25519 && opts.HashFunc() == crypto.Hash(0):
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return Sign(priv, message), nil
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case scheme == ED25519Ph && opts.HashFunc() == crypto.SHA512:
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return SignPh(priv, message, ctx), nil
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case scheme == ED25519Ctx && opts.HashFunc() == crypto.Hash(0) && len(ctx) > 0:
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return SignWithCtx(priv, message, ctx), nil
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default:
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return nil, errors.New("ed25519: bad hash algorithm")
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}
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}
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// GenerateKey generates a public/private key pair using entropy from rand.
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// If rand is nil, crypto/rand.Reader will be used.
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func GenerateKey(rand io.Reader) (PublicKey, PrivateKey, error) {
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if rand == nil {
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rand = cryptoRand.Reader
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}
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seed := make([]byte, SeedSize)
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if _, err := io.ReadFull(rand, seed); err != nil {
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return nil, nil, err
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}
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privateKey := NewKeyFromSeed(seed)
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publicKey := make(PublicKey, PublicKeySize)
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copy(publicKey, privateKey[SeedSize:])
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return publicKey, privateKey, nil
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}
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// NewKeyFromSeed calculates a private key from a seed. It will panic if
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// len(seed) is not SeedSize. This function is provided for interoperability
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// with RFC 8032. RFC 8032's private keys correspond to seeds in this
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// package.
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func NewKeyFromSeed(seed []byte) PrivateKey {
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privateKey := make(PrivateKey, PrivateKeySize)
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newKeyFromSeed(privateKey, seed)
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return privateKey
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}
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func newKeyFromSeed(privateKey, seed []byte) {
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if l := len(seed); l != SeedSize {
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panic("ed25519: bad seed length: " + strconv.Itoa(l))
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}
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var P pointR1
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k := sha512.Sum512(seed)
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clamp(k[:])
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reduceModOrder(k[:paramB], false)
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P.fixedMult(k[:paramB])
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copy(privateKey[:SeedSize], seed)
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_ = P.ToBytes(privateKey[SeedSize:])
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}
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func signAll(signature []byte, privateKey PrivateKey, message, ctx []byte, preHash bool) {
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if l := len(privateKey); l != PrivateKeySize {
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panic("ed25519: bad private key length: " + strconv.Itoa(l))
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}
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H := sha512.New()
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var PHM []byte
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if preHash {
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_, _ = H.Write(message)
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PHM = H.Sum(nil)
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H.Reset()
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} else {
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PHM = message
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}
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// 1. Hash the 32-byte private key using SHA-512.
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_, _ = H.Write(privateKey[:SeedSize])
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h := H.Sum(nil)
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clamp(h[:])
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prefix, s := h[paramB:], h[:paramB]
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// 2. Compute SHA-512(dom2(F, C) || prefix || PH(M))
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H.Reset()
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writeDom(H, ctx, preHash)
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_, _ = H.Write(prefix)
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_, _ = H.Write(PHM)
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r := H.Sum(nil)
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reduceModOrder(r[:], true)
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// 3. Compute the point [r]B.
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var P pointR1
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P.fixedMult(r[:paramB])
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R := (&[paramB]byte{})[:]
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if err := P.ToBytes(R); err != nil {
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panic(err)
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}
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// 4. Compute SHA512(dom2(F, C) || R || A || PH(M)).
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H.Reset()
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writeDom(H, ctx, preHash)
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_, _ = H.Write(R)
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_, _ = H.Write(privateKey[SeedSize:])
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_, _ = H.Write(PHM)
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hRAM := H.Sum(nil)
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reduceModOrder(hRAM[:], true)
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// 5. Compute S = (r + k * s) mod order.
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S := (&[paramB]byte{})[:]
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calculateS(S, r[:paramB], hRAM[:paramB], s)
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// 6. The signature is the concatenation of R and S.
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copy(signature[:paramB], R[:])
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copy(signature[paramB:], S[:])
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}
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// Sign signs the message with privateKey and returns a signature.
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// This function supports the signature variant defined in RFC-8032: Ed25519,
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// also known as the pure version of EdDSA.
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// It will panic if len(privateKey) is not PrivateKeySize.
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func Sign(privateKey PrivateKey, message []byte) []byte {
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signature := make([]byte, SignatureSize)
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signAll(signature, privateKey, message, []byte(""), false)
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return signature
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}
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// SignPh creates a signature of a message with private key and context.
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// This function supports the signature variant defined in RFC-8032: Ed25519ph,
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// meaning it internally hashes the message using SHA-512, and optionally
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// accepts a context string.
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// It will panic if len(privateKey) is not PrivateKeySize.
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// Context could be passed to this function, which length should be no more than
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// ContextMaxSize=255. It can be empty.
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func SignPh(privateKey PrivateKey, message []byte, ctx string) []byte {
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if len(ctx) > ContextMaxSize {
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panic(fmt.Errorf("ed25519: bad context length: %v", len(ctx)))
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}
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signature := make([]byte, SignatureSize)
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signAll(signature, privateKey, message, []byte(ctx), true)
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return signature
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}
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// SignWithCtx creates a signature of a message with private key and context.
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// This function supports the signature variant defined in RFC-8032: Ed25519ctx,
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// meaning it accepts a non-empty context string.
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// It will panic if len(privateKey) is not PrivateKeySize.
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// Context must be passed to this function, which length should be no more than
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// ContextMaxSize=255 and cannot be empty.
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func SignWithCtx(privateKey PrivateKey, message []byte, ctx string) []byte {
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if len(ctx) == 0 || len(ctx) > ContextMaxSize {
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panic(fmt.Errorf("ed25519: bad context length: %v > %v", len(ctx), ContextMaxSize))
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}
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signature := make([]byte, SignatureSize)
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signAll(signature, privateKey, message, []byte(ctx), false)
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return signature
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}
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func verify(public PublicKey, message, signature, ctx []byte, preHash bool) bool {
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if len(public) != PublicKeySize ||
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len(signature) != SignatureSize ||
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!isLessThanOrder(signature[paramB:]) {
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return false
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}
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var P pointR1
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if ok := P.FromBytes(public); !ok {
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return false
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}
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H := sha512.New()
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var PHM []byte
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if preHash {
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_, _ = H.Write(message)
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PHM = H.Sum(nil)
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H.Reset()
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} else {
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PHM = message
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}
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R := signature[:paramB]
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writeDom(H, ctx, preHash)
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_, _ = H.Write(R)
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_, _ = H.Write(public)
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_, _ = H.Write(PHM)
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hRAM := H.Sum(nil)
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reduceModOrder(hRAM[:], true)
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var Q pointR1
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encR := (&[paramB]byte{})[:]
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P.neg()
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Q.doubleMult(&P, signature[paramB:], hRAM[:paramB])
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_ = Q.ToBytes(encR)
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return bytes.Equal(R, encR)
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}
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// VerifyAny returns true if the signature is valid. Failure cases are invalid
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// signature, or when the public key cannot be decoded.
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// This function supports all the three signature variants defined in RFC-8032,
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// namely Ed25519 (or pure EdDSA), Ed25519Ph, and Ed25519Ctx.
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// The opts.HashFunc() must return zero to specify either Ed25519 or Ed25519Ctx
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// variant. This can be achieved by passing crypto.Hash(0) as the value for opts.
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// The opts.HashFunc() must return SHA512 to specify the Ed25519Ph variant.
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// This can be achieved by passing crypto.SHA512 as the value for opts.
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// Use a SignerOptions struct to pass a context string for signing.
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func VerifyAny(public PublicKey, message, signature []byte, opts crypto.SignerOpts) bool {
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var ctx string
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var scheme SchemeID
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if o, ok := opts.(SignerOptions); ok {
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ctx = o.Context
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scheme = o.Scheme
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}
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switch true {
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case scheme == ED25519 && opts.HashFunc() == crypto.Hash(0):
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return Verify(public, message, signature)
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case scheme == ED25519Ph && opts.HashFunc() == crypto.SHA512:
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return VerifyPh(public, message, signature, ctx)
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case scheme == ED25519Ctx && opts.HashFunc() == crypto.Hash(0) && len(ctx) > 0:
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return VerifyWithCtx(public, message, signature, ctx)
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default:
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return false
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}
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}
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// Verify returns true if the signature is valid. Failure cases are invalid
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// signature, or when the public key cannot be decoded.
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// This function supports the signature variant defined in RFC-8032: Ed25519,
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// also known as the pure version of EdDSA.
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func Verify(public PublicKey, message, signature []byte) bool {
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return verify(public, message, signature, []byte(""), false)
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}
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// VerifyPh returns true if the signature is valid. Failure cases are invalid
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// signature, or when the public key cannot be decoded.
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// This function supports the signature variant defined in RFC-8032: Ed25519ph,
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// meaning it internally hashes the message using SHA-512.
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// Context could be passed to this function, which length should be no more than
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// 255. It can be empty.
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func VerifyPh(public PublicKey, message, signature []byte, ctx string) bool {
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return verify(public, message, signature, []byte(ctx), true)
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}
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// VerifyWithCtx returns true if the signature is valid. Failure cases are invalid
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// signature, or when the public key cannot be decoded, or when context is
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// not provided.
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// This function supports the signature variant defined in RFC-8032: Ed25519ctx,
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// meaning it does not handle prehashed messages. Non-empty context string must be
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// provided, and must not be more than 255 of length.
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func VerifyWithCtx(public PublicKey, message, signature []byte, ctx string) bool {
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if len(ctx) == 0 || len(ctx) > ContextMaxSize {
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return false
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}
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return verify(public, message, signature, []byte(ctx), false)
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}
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func clamp(k []byte) {
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k[0] &= 248
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k[paramB-1] = (k[paramB-1] & 127) | 64
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}
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// isLessThanOrder returns true if 0 <= x < order.
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func isLessThanOrder(x []byte) bool {
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i := len(order) - 1
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for i > 0 && x[i] == order[i] {
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i--
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}
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return x[i] < order[i]
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}
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func writeDom(h io.Writer, ctx []byte, preHash bool) {
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dom2 := "SigEd25519 no Ed25519 collisions"
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if len(ctx) > 0 {
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_, _ = h.Write([]byte(dom2))
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if preHash {
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_, _ = h.Write([]byte{byte(0x01), byte(len(ctx))})
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} else {
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_, _ = h.Write([]byte{byte(0x00), byte(len(ctx))})
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}
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_, _ = h.Write(ctx)
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} else if preHash {
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_, _ = h.Write([]byte(dom2))
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_, _ = h.Write([]byte{0x01, 0x00})
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}
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}
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