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264 lines
7.5 KiB
Go
264 lines
7.5 KiB
Go
// Copyright (c) 2014 - Gustavo Niemeyer <gustavo@niemeyer.net>
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//
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// All rights reserved.
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//
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// Redistribution and use in source and binary forms, with or without
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// modification, are permitted provided that the following conditions are met:
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//
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// 1. Redistributions of source code must retain the above copyright notice, this
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// list of conditions and the following disclaimer.
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// 2. Redistributions in binary form must reproduce the above copyright notice,
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// this list of conditions and the following disclaimer in the documentation
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// and/or other materials provided with the distribution.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
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// ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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// WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
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// ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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// (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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// LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
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// ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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// SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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// Package scram implements a SCRAM-{SHA-1,etc} client per RFC5802.
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//
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// http://tools.ietf.org/html/rfc5802
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//
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package scram
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import (
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"bytes"
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"crypto/hmac"
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"crypto/rand"
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"encoding/base64"
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"fmt"
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"hash"
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"strconv"
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"strings"
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)
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// Client implements a SCRAM-* client (SCRAM-SHA-1, SCRAM-SHA-256, etc).
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//
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// A Client may be used within a SASL conversation with logic resembling:
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//
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// var in []byte
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// var client = scram.NewClient(sha1.New, user, pass)
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// for client.Step(in) {
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// out := client.Out()
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// // send out to server
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// in := serverOut
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// }
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// if client.Err() != nil {
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// // auth failed
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// }
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//
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type Client struct {
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newHash func() hash.Hash
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user string
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pass string
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step int
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out bytes.Buffer
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err error
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clientNonce []byte
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serverNonce []byte
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saltedPass []byte
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authMsg bytes.Buffer
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}
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// NewClient returns a new SCRAM-* client with the provided hash algorithm.
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//
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// For SCRAM-SHA-256, for example, use:
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//
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// client := scram.NewClient(sha256.New, user, pass)
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//
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func NewClient(newHash func() hash.Hash, user, pass string) *Client {
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c := &Client{
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newHash: newHash,
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user: user,
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pass: pass,
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}
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c.out.Grow(256)
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c.authMsg.Grow(256)
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return c
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}
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// Out returns the data to be sent to the server in the current step.
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func (c *Client) Out() []byte {
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if c.out.Len() == 0 {
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return nil
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}
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return c.out.Bytes()
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}
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// Err returns the error that ocurred, or nil if there were no errors.
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func (c *Client) Err() error {
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return c.err
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}
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// SetNonce sets the client nonce to the provided value.
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// If not set, the nonce is generated automatically out of crypto/rand on the first step.
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func (c *Client) SetNonce(nonce []byte) {
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c.clientNonce = nonce
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}
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var escaper = strings.NewReplacer("=", "=3D", ",", "=2C")
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// Step processes the incoming data from the server and makes the
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// next round of data for the server available via Client.Out.
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// Step returns false if there are no errors and more data is
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// still expected.
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func (c *Client) Step(in []byte) bool {
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c.out.Reset()
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if c.step > 2 || c.err != nil {
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return false
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}
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c.step++
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switch c.step {
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case 1:
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c.err = c.step1(in)
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case 2:
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c.err = c.step2(in)
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case 3:
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c.err = c.step3(in)
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}
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return c.step > 2 || c.err != nil
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}
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func (c *Client) step1(in []byte) error {
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if len(c.clientNonce) == 0 {
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const nonceLen = 16
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buf := make([]byte, nonceLen+b64.EncodedLen(nonceLen))
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if _, err := rand.Read(buf[:nonceLen]); err != nil {
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return fmt.Errorf("cannot read random SCRAM-SHA-256 nonce from operating system: %v", err)
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}
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c.clientNonce = buf[nonceLen:]
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b64.Encode(c.clientNonce, buf[:nonceLen])
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}
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c.authMsg.WriteString("n=")
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escaper.WriteString(&c.authMsg, c.user)
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c.authMsg.WriteString(",r=")
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c.authMsg.Write(c.clientNonce)
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c.out.WriteString("n,,")
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c.out.Write(c.authMsg.Bytes())
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return nil
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}
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var b64 = base64.StdEncoding
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func (c *Client) step2(in []byte) error {
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c.authMsg.WriteByte(',')
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c.authMsg.Write(in)
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fields := bytes.Split(in, []byte(","))
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if len(fields) != 3 {
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return fmt.Errorf("expected 3 fields in first SCRAM-SHA-256 server message, got %d: %q", len(fields), in)
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}
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if !bytes.HasPrefix(fields[0], []byte("r=")) || len(fields[0]) < 2 {
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return fmt.Errorf("server sent an invalid SCRAM-SHA-256 nonce: %q", fields[0])
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}
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if !bytes.HasPrefix(fields[1], []byte("s=")) || len(fields[1]) < 6 {
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return fmt.Errorf("server sent an invalid SCRAM-SHA-256 salt: %q", fields[1])
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}
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if !bytes.HasPrefix(fields[2], []byte("i=")) || len(fields[2]) < 6 {
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return fmt.Errorf("server sent an invalid SCRAM-SHA-256 iteration count: %q", fields[2])
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}
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c.serverNonce = fields[0][2:]
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if !bytes.HasPrefix(c.serverNonce, c.clientNonce) {
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return fmt.Errorf("server SCRAM-SHA-256 nonce is not prefixed by client nonce: got %q, want %q+\"...\"", c.serverNonce, c.clientNonce)
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}
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salt := make([]byte, b64.DecodedLen(len(fields[1][2:])))
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n, err := b64.Decode(salt, fields[1][2:])
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if err != nil {
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return fmt.Errorf("cannot decode SCRAM-SHA-256 salt sent by server: %q", fields[1])
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}
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salt = salt[:n]
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iterCount, err := strconv.Atoi(string(fields[2][2:]))
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if err != nil {
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return fmt.Errorf("server sent an invalid SCRAM-SHA-256 iteration count: %q", fields[2])
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}
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c.saltPassword(salt, iterCount)
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c.authMsg.WriteString(",c=biws,r=")
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c.authMsg.Write(c.serverNonce)
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c.out.WriteString("c=biws,r=")
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c.out.Write(c.serverNonce)
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c.out.WriteString(",p=")
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c.out.Write(c.clientProof())
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return nil
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}
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func (c *Client) step3(in []byte) error {
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var isv, ise bool
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var fields = bytes.Split(in, []byte(","))
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if len(fields) == 1 {
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isv = bytes.HasPrefix(fields[0], []byte("v="))
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ise = bytes.HasPrefix(fields[0], []byte("e="))
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}
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if ise {
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return fmt.Errorf("SCRAM-SHA-256 authentication error: %s", fields[0][2:])
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} else if !isv {
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return fmt.Errorf("unsupported SCRAM-SHA-256 final message from server: %q", in)
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}
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if !bytes.Equal(c.serverSignature(), fields[0][2:]) {
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return fmt.Errorf("cannot authenticate SCRAM-SHA-256 server signature: %q", fields[0][2:])
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}
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return nil
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}
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func (c *Client) saltPassword(salt []byte, iterCount int) {
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mac := hmac.New(c.newHash, []byte(c.pass))
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mac.Write(salt)
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mac.Write([]byte{0, 0, 0, 1})
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ui := mac.Sum(nil)
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hi := make([]byte, len(ui))
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copy(hi, ui)
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for i := 1; i < iterCount; i++ {
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mac.Reset()
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mac.Write(ui)
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mac.Sum(ui[:0])
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for j, b := range ui {
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hi[j] ^= b
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}
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}
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c.saltedPass = hi
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}
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func (c *Client) clientProof() []byte {
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mac := hmac.New(c.newHash, c.saltedPass)
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mac.Write([]byte("Client Key"))
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clientKey := mac.Sum(nil)
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hash := c.newHash()
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hash.Write(clientKey)
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storedKey := hash.Sum(nil)
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mac = hmac.New(c.newHash, storedKey)
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mac.Write(c.authMsg.Bytes())
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clientProof := mac.Sum(nil)
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for i, b := range clientKey {
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clientProof[i] ^= b
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}
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clientProof64 := make([]byte, b64.EncodedLen(len(clientProof)))
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b64.Encode(clientProof64, clientProof)
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return clientProof64
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}
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func (c *Client) serverSignature() []byte {
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mac := hmac.New(c.newHash, c.saltedPass)
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mac.Write([]byte("Server Key"))
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serverKey := mac.Sum(nil)
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mac = hmac.New(c.newHash, serverKey)
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mac.Write(c.authMsg.Bytes())
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serverSignature := mac.Sum(nil)
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encoded := make([]byte, b64.EncodedLen(len(serverSignature)))
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b64.Encode(encoded, serverSignature)
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return encoded
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}
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