refactor checks, IP-ban incorrect passphrases, renames

- s/assword/assphrase/, typo fixes
- bans are checked separately from public keys
- an incorrect passphrase results in a one-minute IP ban
- whitelists no longer override bans (i.e. you can get banned if you're 
whitelisted)

auth.go

@@ -19,9 +19,12 @@ import (
 // when whitelisting is enabled.
 var ErrNotWhitelisted = errors.New("not whitelisted")
 
-// ErrBanned is the error returned when a key is checked that is banned.
+// ErrBanned is the error returned when a client is banned.
 var ErrBanned = errors.New("banned")
 
+// ErrIncorrectPassphrase is the error returned when a provided passphrase is incorrect.
+var ErrIncorrectPassphrase = errors.New("incorrect passphrase")
+
 // newAuthKey returns string from an ssh.PublicKey used to index the key in our lookup.
 func newAuthKey(key ssh.PublicKey) string {
 	if key == nil {
@@ -45,17 +48,17 @@ func newAuthAddr(addr net.Addr) string {
 }
 
 // Auth stores lookups for bans, whitelists, and ops. It implements the sshd.Auth interface.
-// If the contained password is not empty, it complements a whitelist.
+// If the contained passphrase is not empty, it complements a whitelist.
 type Auth struct {
-	passwordHash []byte
-	bannedAddr   *set.Set
-	bannedClient *set.Set
-	banned       *set.Set
-	whitelist    *set.Set
-	ops          *set.Set
+	passphraseHash []byte
+	bannedAddr     *set.Set
+	bannedClient   *set.Set
+	banned         *set.Set
+	whitelist      *set.Set
+	ops            *set.Set
 }
 
-// NewAuth creates a Auth, optionally with a password.
+// NewAuth creates a new empty Auth.
 func NewAuth() *Auth {
 	return &Auth{
 		bannedAddr:   set.New(),
@@ -66,40 +69,31 @@ func NewAuth() *Auth {
 	}
 }
 
-// SetPassword anables password authentication with the given password.
-// If an emty password is geiven, disable password authentication.
-func (a *Auth) SetPassword(password string) {
-	if password == "" {
-		a.passwordHash = nil
+// SetPassphrase enables passphrase authentication with the given passphrase.
+// If an empty passphrase is given, disable passphrase authentication.
+func (a *Auth) SetPassphrase(passphrase string) {
+	if passphrase == "" {
+		a.passphraseHash = nil
 	} else {
-		hashArray := sha256.Sum256([]byte(password))
-		a.passwordHash = hashArray[:]
+		hashArray := sha256.Sum256([]byte(passphrase))
+		a.passphraseHash = hashArray[:]
 	}
 }
 
 // AllowAnonymous determines if anonymous users are permitted.
 func (a *Auth) AllowAnonymous() bool {
-	return a.whitelist.Len() == 0 && a.passwordHash == nil
+	return a.whitelist.Len() == 0 && a.passphraseHash == nil
 }
 
-// AcceptPassword determines if password authentication is accepted.
-func (a *Auth) AcceptPassword() bool {
-	return a.passwordHash != nil
+// AcceptPassphrase determines if passphrase authentication is accepted.
+func (a *Auth) AcceptPassphrase() bool {
+	return a.passphraseHash != nil
 }
 
-// Check determines if a pubkey fingerprint is permitted.
-func (a *Auth) Check(addr net.Addr, key ssh.PublicKey, clientVersion string) error {
+// CheckBans checks IP, key and client bans.
+func (a *Auth) CheckBans(addr net.Addr, key ssh.PublicKey, clientVersion string) error {
 	authkey := newAuthKey(key)
 
-	if !a.AllowAnonymous() {
-		// Only check whitelist if we don't allow everyone to connect.
-		whitelisted := a.whitelist.In(authkey)
-		if !whitelisted {
-			return ErrNotWhitelisted
-		}
-		return nil
-	}
-
 	var banned bool
 	if authkey != "" {
 		banned = a.banned.In(authkey)
@@ -118,14 +112,25 @@ func (a *Auth) Check(addr net.Addr, key ssh.PublicKey, clientVersion string) err
 	return nil
 }
 
-// CheckPassword determines if a password is permitted.
-func (a *Auth) CheckPassword(password string) error {
-	if !a.AcceptPassword() {
-		return errors.New("passwords not accepted") // this should never happen
+// CheckPubkey determines if a pubkey fingerprint is permitted.
+func (a *Auth) CheckPubkey(key ssh.PublicKey) error {
+	authkey := newAuthKey(key)
+	whitelisted := a.whitelist.In(authkey)
+	if a.AllowAnonymous() || whitelisted {
+		return nil
+	} else {
+		return ErrNotWhitelisted
 	}
-	passedPasswordhash := sha256.Sum256([]byte(password))
-	if subtle.ConstantTimeCompare(passedPasswordhash[:], a.passwordHash) == 0 {
-		return errors.New("incorrect password")
+}
+
+// CheckPassphrase determines if a passphrase is permitted.
+func (a *Auth) CheckPassphrase(passphrase string) error {
+	if !a.AcceptPassphrase() {
+		return errors.New("passphrases not accepted") // this should never happen
+	}
+	passedPassphraseHash := sha256.Sum256([]byte(passphrase))
+	if subtle.ConstantTimeCompare(passedPassphraseHash[:], a.passphraseHash) == 0 {
+		return ErrIncorrectPassphrase
 	}
 	return nil
 }

auth_test.go

@@ -28,7 +28,7 @@ func TestAuthWhitelist(t *testing.T) {
 	}
 
 	auth := NewAuth()
-	err = auth.Check(nil, key, "")
+	err = auth.CheckPubkey(key)
 	if err != nil {
 		t.Error("Failed to permit in default state:", err)
 	}
@@ -44,7 +44,7 @@ func TestAuthWhitelist(t *testing.T) {
 		t.Error("Clone key does not match.")
 	}
 
-	err = auth.Check(nil, keyClone, "")
+	err = auth.CheckPubkey(keyClone)
 	if err != nil {
 		t.Error("Failed to permit whitelisted:", err)
 	}
@@ -54,42 +54,42 @@ func TestAuthWhitelist(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	err = auth.Check(nil, key2, "")
+	err = auth.CheckPubkey(key2)
 	if err == nil {
 		t.Error("Failed to restrict not whitelisted:", err)
 	}
 }
 
-func TestAuthPasswords(t *testing.T) {
+func TestAuthPassphrases(t *testing.T) {
 	auth := NewAuth()
 
-	if auth.AcceptPassword() {
-		t.Error("Doesn't known it won't accept passwords.")
+	if auth.AcceptPassphrase() {
+		t.Error("Doesn't known it won't accept passphrases.")
 	}
-	auth.SetPassword("")
-	if auth.AcceptPassword() {
-		t.Error("Doesn't known it won't accept passwords.")
+	auth.SetPassphrase("")
+	if auth.AcceptPassphrase() {
+		t.Error("Doesn't known it won't accept passphrases.")
 	}
 
-	err := auth.CheckPassword("Pa$$w0rd")
+	err := auth.CheckPassphrase("Pa$$w0rd")
 	if err == nil {
-		t.Error("Failed to deny without password:", err)
+		t.Error("Failed to deny without passphrase:", err)
 	}
 
-	auth.SetPassword("Pa$$w0rd")
+	auth.SetPassphrase("Pa$$w0rd")
 
-	err = auth.CheckPassword("Pa$$w0rd")
+	err = auth.CheckPassphrase("Pa$$w0rd")
 	if err != nil {
-		t.Error("Failed to allow vaild password:", err)
+		t.Error("Failed to allow vaild passphrase:", err)
 	}
 
-	err = auth.CheckPassword("something else")
+	err = auth.CheckPassphrase("something else")
 	if err == nil {
-		t.Error("Failed to restrict wrong password:", err)
+		t.Error("Failed to restrict wrong passphrase:", err)
 	}
 
-	auth.SetPassword("")
-	if auth.AcceptPassword() {
-		t.Error("Didn't clear password.")
+	auth.SetPassphrase("")
+	if auth.AcceptPassphrase() {
+		t.Error("Didn't clear passphrase.")
 	}
 }

cmd/ssh-chat/cmd.go

@@ -135,7 +135,7 @@ func main() {
 	host.Version = Version
 
 	if options.Passphrase != "" {
-		auth.SetPassword(options.Passphrase)
+		auth.SetPassphrase(options.Passphrase)
 	}
 
 	err = fromFile(options.Admin, func(line []byte) error {

sshd/auth.go

@@ -5,21 +5,26 @@ import (
 	"encoding/base64"
 	"errors"
 	"net"
+	"time"
 
 	"github.com/shazow/ssh-chat/internal/sanitize"
 	"golang.org/x/crypto/ssh"
 )
 
-// Auth is used to authenticate connections based on public keys.
+// Auth is used to authenticate connections.
 type Auth interface {
 	// Whether to allow connections without a public key.
 	AllowAnonymous() bool
-	// If password authtication is accepted
-	AcceptPassword() bool
-	// Given address and public key and client agent string, returns nil if the connection should be allowed.
-	Check(net.Addr, ssh.PublicKey, string) error
-	// Given a password, returns nil if the connection should be allowed
-	CheckPassword(string) error
+	// If passphrase authentication is accepted
+	AcceptPassphrase() bool
+	// Given address and public key and client agent string, returns nil if the connection is not banned.
+	CheckBans(net.Addr, ssh.PublicKey, string) error
+	// Given a public key, returns nil if the connection should be allowed.
+	CheckPubkey(ssh.PublicKey) error
+	// Given a passphrase, returns nil if the connection should be allowed.
+	CheckPassphrase(string) error
+	// BanAddr bans an IP address for the specified amount of time.
+	BanAddr(net.Addr, time.Duration)
 }
 
 // MakeAuth makes an ssh.ServerConfig which performs authentication against an Auth implementation.
@@ -29,7 +34,11 @@ func MakeAuth(auth Auth) *ssh.ServerConfig {
 		NoClientAuth: false,
 		// Auth-related things should be constant-time to avoid timing attacks.
 		PublicKeyCallback: func(conn ssh.ConnMetadata, key ssh.PublicKey) (*ssh.Permissions, error) {
-			err := auth.Check(conn.RemoteAddr(), key, sanitize.Data(string(conn.ClientVersion()), 64))
+			err := auth.CheckBans(conn.RemoteAddr(), key, sanitize.Data(string(conn.ClientVersion()), 64))
+			if err != nil {
+				return nil, err
+			}
+			err = auth.CheckPubkey(key)
 			if err != nil {
 				return nil, err
 			}
@@ -43,20 +52,26 @@ func MakeAuth(auth Auth) *ssh.ServerConfig {
 		// avoid preventing the client from including a pubkey in the user
 		// identification.
 		KeyboardInteractiveCallback: func(conn ssh.ConnMetadata, challenge ssh.KeyboardInteractiveChallenge) (*ssh.Permissions, error) {
-			var err error
-			if auth.AcceptPassword() {
+			err := auth.CheckBans(conn.RemoteAddr(), nil, sanitize.Data(string(conn.ClientVersion()), 64))
+			if err != nil {
+				return nil, err
+			}
+			if auth.AcceptPassphrase() {
 				var answers []string
 				answers, err = challenge("", "", []string{"Passphrase required to connect: "}, []bool{true})
 				if err == nil {
 					if len(answers) != 1 {
-						err = errors.New("didn't get password")
+						err = errors.New("didn't get passphrase")
 					} else {
-						err = auth.CheckPassword(answers[0])
-						// TODO: some kind of brute force throttling here?
+						err = auth.CheckPassphrase(answers[0])
+						if err != nil {
+							// TODO: make rate-limiting configurable
+							auth.BanAddr(conn.RemoteAddr(), time.Minute * 1)
+						}
 					}
 				}
-			} else {
-				err = auth.Check(conn.RemoteAddr(), nil, sanitize.Data(string(conn.ClientVersion()), 64))
+			} else if !auth.AllowAnonymous(){
+				err = errors.New("public key authentication required")
 			}
 			return nil, err
 		},

sshd/client_test.go

@@ -4,6 +4,7 @@ import (
 	"errors"
 	"net"
 	"testing"
+	"time"
 
 	"golang.org/x/crypto/ssh"
 )
@@ -15,15 +16,19 @@ type RejectAuth struct{}
 func (a RejectAuth) AllowAnonymous() bool {
 	return false
 }
-func (a RejectAuth) AcceptPassword() bool {
+func (a RejectAuth) AcceptPassphrase() bool {
 	return false
 }
-func (a RejectAuth) Check(net.Addr, ssh.PublicKey, string) error {
+func (a RejectAuth) CheckBans(addr net.Addr, key ssh.PublicKey, clientVersion string) error {
 	return errRejectAuth
 }
-func (a RejectAuth) CheckPassword(string) error {
+func (a RejectAuth) CheckPubkey(ssh.PublicKey) error {
 	return errRejectAuth
 }
+func (a RejectAuth) CheckPassphrase(string) error {
+	return errRejectAuth
+}
+func (a RejectAuth) BanAddr(net.Addr, time.Duration) {}
 
 func TestClientReject(t *testing.T) {
 	signer, err := NewRandomSigner(512)