packer-cn/helper/ssh/key_pair_test.go

package ssh

import (
	"bytes"
	"crypto/dsa"
	"crypto/ecdsa"
	"crypto/rsa"
	"fmt"
	"testing"

	"github.com/hashicorp/packer/common/uuid"
	"golang.org/x/crypto/ed25519"
	gossh "golang.org/x/crypto/ssh"
)

const (
	pemRsa1024 = `-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----
`
	pemRsa2048 = `-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----
`
	pemOpenSshRsa1024 = `-----BEGIN OPENSSH PRIVATE KEY-----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=

-----END OPENSSH PRIVATE KEY-----
`
	pemOpenSshRsa2048 = `-----BEGIN OPENSSH PRIVATE KEY-----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-----END OPENSSH PRIVATE KEY-----
`
	pemDsa = `-----BEGIN DSA PRIVATE KEY-----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-----END DSA PRIVATE KEY-----
`
	pemEcdsa384 = `-----BEGIN EC PRIVATE KEY-----
MIGkAgEBBDAjuEIlmFyhGjFtJoAwD420FuPAjIknN3YwDZL4cfMFpB4YAK+7QVLs
coAJ/ADuT7OgBwYFK4EEACKhZANiAASeXKyBr2prr4f4aOsM4dtVikYOUIL3yYnb
GFOy7yHmauCnkIB48paXpvRE5m53Q8zgu7vkz/z9tcMBcC0GzpY3Sef37fmgTUuZ
AJuJp36DMBdQel+j51TcQ79sizxCayg=
-----END EC PRIVATE KEY-----
`
	pemEcdsa521 = `-----BEGIN EC PRIVATE KEY-----
MIHcAgEBBEIBVCiwcf/did2vCIu3aMe7OeTD35PULm0hqmfkAK9OKIosi/DjOFfA
8h99rVNPaf+Cx/JNmEzR4bZNnYDyilSRCr+gBwYFK4EEACOhgYkDgYYABABHBMLP
XbQoRF31ZGIeUj9jt9GqKES1dLBtGDEQSiiZFouL4tEIW7NfIZDpOIkA0khNcO8N
xH6eylg0XOgcr01GRwCjY5VOapOahtn63SpajPGeKk+46F2dULIwrov9tWQuYNa3
P50N8j3rx6fAdgyDENOcCJlfNdNcySvkH4bgL1xcsw==
-----END EC PRIVATE KEY-----
`
	pemOpenSshEd25519 = `-----BEGIN OPENSSH PRIVATE KEY-----
b3BlbnNzaC1rZXktdjEAAAAABG5vbmUAAAAEbm9uZQAAAAAAAAABAAAAMwAAAAtzc2gtZW
QyNTUxOQAAACAUftPhZQN17kAlThiiWJEgJvddm/pUhHvgrHUtpuYFOQAAAKjN+UhDzflI
QwAAAAtzc2gtZWQyNTUxOQAAACAUftPhZQN17kAlThiiWJEgJvddm/pUhHvgrHUtpuYFOQ
AAAEANXlEZdNU03RMmj77O2ojWh06Hbj8/qQ++H5wkt688NBR+0+FlA3XuQCVOGKJYkSAm
912b+lSEe+CsdS2m5gU5AAAAImNocmlzQHBvZXRhc3Rlci5jb3JwLm11dHVhbGluay5uZX
QBAgM=
-----END OPENSSH PRIVATE KEY-----
`
)

func TestNewKeyPair_Default(t *testing.T) {
	kp, err := NewKeyPair(CreateKeyPairConfig{})
	if err != nil {
		t.Fatal(err.Error())
	}

	err = verifyEcdsaKeyPair(kp, expectedData{
		bits: 521,
	})
	if err != nil {
		t.Fatal(err.Error())
	}
}

func TestNewKeyPair_ECDSA_Default(t *testing.T) {
	kp, err := NewKeyPair(CreateKeyPairConfig{
		Type: Ecdsa,
	})
	if err != nil {
		t.Fatal(err.Error())
	}

	err = verifyEcdsaKeyPair(kp, expectedData{
		bits: 521,
	})
	if err != nil {
		t.Fatal(err.Error())
	}
}

func TestNewKeyPair_ECDSA_Positive(t *testing.T) {
	for _, bits := range []int{521, 384, 256} {
		config := CreateKeyPairConfig{
			Type:    Ecdsa,
			Bits:    bits,
			Comment: uuid.TimeOrderedUUID(),
		}

		kp, err := NewKeyPair(config)
		if err != nil {
			t.Fatal(err.Error())
		}

		err = verifyEcdsaKeyPair(kp, expectedData{
			bits:    bits,
			comment: config.Comment,
		})
		if err != nil {
			t.Fatal(err.Error())
		}
	}
}

func TestNewKeyPair_ECDSA_Negative(t *testing.T) {
	for _, bits := range []int{224, 1, 2, 3} {
		_, err := NewKeyPair(CreateKeyPairConfig{
			Type: Ecdsa,
			Bits: bits,
		})
		if err == nil {
			t.Fatalf("expected key pair generation to fail for %d bits", bits)
		}
	}
}

func TestNewKeyPair_RSA_Positive(t *testing.T) {
	for _, bits := range []int{4096, 2048} {
		config := CreateKeyPairConfig{
			Type:    Rsa,
			Bits:    bits,
			Comment: uuid.TimeOrderedUUID(),
		}

		kp, err := NewKeyPair(config)
		if err != nil {
			t.Fatal(err.Error())
		}

		err = verifyRsaKeyPair(kp, expectedData{
			bits:    config.Bits,
			comment: config.Comment,
		})
		if err != nil {
			t.Fatal(err.Error())
		}
	}
}

func TestKeyPairFromPrivateKey(t *testing.T) {
	m := map[string]fromPrivateExpectedData{
		pemRsa1024: {
			t: Rsa,
			d: expectedData{
				bits: 1024,
			},
		},
		pemRsa2048: {
			t: Rsa,
			d: expectedData{
				bits: 2048,
			},
		},
		pemOpenSshRsa1024: {
			t: Rsa,
			d: expectedData{
				bits: 1024,
			},
		},
		pemOpenSshRsa2048: {
			t: Rsa,
			d: expectedData{
				bits: 2048,
			},
		},
		pemDsa: {
			t: Dsa,
			d: expectedData{
				bits: 1024,
			},
		},
		pemEcdsa384: {
			t: Ecdsa,
			d: expectedData{
				bits: 384,
			},
		},
		pemEcdsa521: {
			t: Ecdsa,
			d: expectedData{
				bits: 521,
			},
		},
		pemOpenSshEd25519: {
			t: Ed25519,
			d: expectedData{
				bits: 256,
			},
		},
	}

	for rawPrivateKey, expected := range m {
		kp, err := KeyPairFromPrivateKey(FromPrivateKeyConfig{
			RawPrivateKeyPemBlock: []byte(rawPrivateKey),
		})
		if err != nil {
			t.Fatal(err.Error())
		}

		switch expected.t {
		case Dsa:
			err = verifyDsaKeyPair(kp, expected)
		case Ecdsa:
			err = verifyEcdsaKeyPair(kp, expected.d)
		case Ed25519:
			err = verifyEd25519KeyPair(kp, expected)
		case Rsa:
			err = verifyRsaKeyPair(kp, expected.d)
		default:
			err = fmt.Errorf("unexected SSH key pair type %s", expected.t.String())
		}
		if err != nil {
			t.Fatal(err.Error())
		}
	}
}

type fromPrivateExpectedData struct {
	t KeyPairType
	d expectedData
}

type expectedData struct {
	bits    int
	comment string
}

func verifyEcdsaKeyPair(kp KeyPair, e expectedData) error {
	privateKey, err := gossh.ParseRawPrivateKey(kp.PrivateKeyPemBlock)
	if err != nil {
		return err
	}

	pk, ok := privateKey.(*ecdsa.PrivateKey)
	if !ok {
		return fmt.Errorf("private key should be *ecdsa.PrivateKey")
	}

	if pk.Curve.Params().BitSize != e.bits {
		return fmt.Errorf("bit size should be %d - got %d", e.bits, pk.Curve.Params().BitSize)
	}

	publicKey, err := gossh.NewPublicKey(&pk.PublicKey)
	if err != nil {
		return err
	}

	expectedBytes := bytes.TrimSuffix(gossh.MarshalAuthorizedKey(publicKey), []byte("\n"))
	if len(e.comment) > 0 {
		expectedBytes = append(expectedBytes, ' ')
		expectedBytes = append(expectedBytes, e.comment...)
	}

	if !bytes.Equal(expectedBytes, kp.PublicKeyAuthorizedKeysLine) {
		return fmt.Errorf("authorized keys line should be:\n'%s'\nGot:\n'%s'",
			string(expectedBytes), string(kp.PublicKeyAuthorizedKeysLine))
	}

	return nil
}

func verifyRsaKeyPair(kp KeyPair, e expectedData) error {
	privateKey, err := gossh.ParseRawPrivateKey(kp.PrivateKeyPemBlock)
	if err != nil {
		return err
	}

	pk, ok := privateKey.(*rsa.PrivateKey)
	if !ok {
		return fmt.Errorf("private key should be *rsa.PrivateKey")
	}

	if pk.N.BitLen() != e.bits {
		return fmt.Errorf("bit size should be %d - got %d", e.bits, pk.N.BitLen())
	}

	publicKey, err := gossh.NewPublicKey(&pk.PublicKey)
	if err != nil {
		return err
	}

	expectedBytes := bytes.TrimSuffix(gossh.MarshalAuthorizedKey(publicKey), []byte("\n"))
	if len(e.comment) > 0 {
		expectedBytes = append(expectedBytes, ' ')
		expectedBytes = append(expectedBytes, e.comment...)
	}

	if !bytes.Equal(expectedBytes, kp.PublicKeyAuthorizedKeysLine) {
		return fmt.Errorf("authorized keys line should be:\n'%s'\nGot:\n'%s'",
			string(expectedBytes), string(kp.PublicKeyAuthorizedKeysLine))
	}

	return nil
}

func verifyDsaKeyPair(kp KeyPair, e fromPrivateExpectedData) error {
	privateKey, err := gossh.ParseRawPrivateKey(kp.PrivateKeyPemBlock)
	if err != nil {
		return err
	}

	pk, ok := privateKey.(*dsa.PrivateKey)
	if !ok {
		return fmt.Errorf("private key should be *rsa.PrivateKey")
	}

	publicKey, err := gossh.NewPublicKey(&pk.PublicKey)
	if err != nil {
		return err
	}

	expectedBytes := bytes.TrimSuffix(gossh.MarshalAuthorizedKey(publicKey), []byte("\n"))
	if len(e.d.comment) > 0 {
		expectedBytes = append(expectedBytes, ' ')
		expectedBytes = append(expectedBytes, e.d.comment...)
	}

	if !bytes.Equal(expectedBytes, kp.PublicKeyAuthorizedKeysLine) {
		return fmt.Errorf("authorized keys line should be:\n'%s'\nGot:\n'%s'",
			string(expectedBytes), string(kp.PublicKeyAuthorizedKeysLine))
	}

	return nil
}

func verifyEd25519KeyPair(kp KeyPair, e fromPrivateExpectedData) error {
	privateKey, err := gossh.ParseRawPrivateKey(kp.PrivateKeyPemBlock)
	if err != nil {
		return err
	}

	pk, ok := privateKey.(*ed25519.PrivateKey)
	if !ok {
		return fmt.Errorf("private key should be *rsa.PrivateKey")
	}

	publicKey, err := gossh.NewPublicKey(pk.Public())
	if err != nil {
		return err
	}

	expectedBytes := bytes.TrimSuffix(gossh.MarshalAuthorizedKey(publicKey), []byte("\n"))
	if len(e.d.comment) > 0 {
		expectedBytes = append(expectedBytes, ' ')
		expectedBytes = append(expectedBytes, e.d.comment...)
	}

	if !bytes.Equal(expectedBytes, kp.PublicKeyAuthorizedKeysLine) {
		return fmt.Errorf("authorized keys line should be:\n'%s'\nGot:\n'%s'",
			string(expectedBytes), string(kp.PublicKeyAuthorizedKeysLine))
	}

	return nil
}