message.go

package jwe

import (
	"context"
	"crypto/ecdsa"
	"fmt"

	"github.com/lestrrat-go/jwx/internal/json"
	"github.com/lestrrat-go/jwx/internal/pool"
	"github.com/lestrrat-go/jwx/jwk"

	"github.com/lestrrat-go/jwx/internal/base64"
	"github.com/lestrrat-go/jwx/jwa"
	"github.com/pkg/errors"
)

// NewRecipient creates a Recipient object
func NewRecipient() Recipient {
	return &stdRecipient{
		headers: NewHeaders(),
	}
}

func (r *stdRecipient) SetHeaders(h Headers) error {
	r.headers = h
	return nil
}

func (r *stdRecipient) SetEncryptedKey(v []byte) error {
	r.encryptedKey = v
	return nil
}

func (r *stdRecipient) Headers() Headers {
	return r.headers
}

func (r *stdRecipient) EncryptedKey() []byte {
	return r.encryptedKey
}

type recipientMarshalProxy struct {
	Headers      Headers `json:"header"`
	EncryptedKey string  `json:"encrypted_key"`
}

func (r *stdRecipient) UnmarshalJSON(buf []byte) error {
	var proxy recipientMarshalProxy
	proxy.Headers = NewHeaders()
	if err := json.Unmarshal(buf, &proxy); err != nil {
		return errors.Wrap(err, `failed to unmarshal json into recipient`)
	}

	r.headers = proxy.Headers
	decoded, err := base64.DecodeString(proxy.EncryptedKey)
	if err != nil {
		return errors.Wrap(err, `failed to decode "encrypted_key"`)
	}
	r.encryptedKey = decoded
	return nil
}

func (r *stdRecipient) MarshalJSON() ([]byte, error) {
	buf := pool.GetBytesBuffer()
	defer pool.ReleaseBytesBuffer(buf)

	buf.WriteString(`{"header":`)
	hdrbuf, err := r.headers.MarshalJSON()
	if err != nil {
		return nil, errors.Wrap(err, `failed to marshal recipient header`)
	}
	buf.Write(hdrbuf)
	buf.WriteString(`,"encrypted_key":"`)
	buf.WriteString(base64.EncodeToString(r.encryptedKey))
	buf.WriteString(`"}`)

	ret := make([]byte, buf.Len())
	copy(ret, buf.Bytes())
	return ret, nil
}

// NewMessage creates a new message
func NewMessage() *Message {
	return &Message{}
}

func (m *Message) AuthenticatedData() []byte {
	return m.authenticatedData
}

func (m *Message) CipherText() []byte {
	return m.cipherText
}

func (m *Message) InitializationVector() []byte {
	return m.initializationVector
}

func (m *Message) Tag() []byte {
	return m.tag
}

func (m *Message) ProtectedHeaders() Headers {
	return m.protectedHeaders
}

func (m *Message) Recipients() []Recipient {
	return m.recipients
}

func (m *Message) UnprotectedHeaders() Headers {
	return m.unprotectedHeaders
}

const (
	AuthenticatedDataKey    = "aad"
	CipherTextKey           = "ciphertext"
	CountKey                = "p2c"
	InitializationVectorKey = "iv"
	ProtectedHeadersKey     = "protected"
	RecipientsKey           = "recipients"
	SaltKey                 = "p2s"
	TagKey                  = "tag"
	UnprotectedHeadersKey   = "unprotected"
	HeadersKey              = "header"
	EncryptedKeyKey         = "encrypted_key"
)

func (m *Message) Set(k string, v interface{}) error {
	switch k {
	case AuthenticatedDataKey:
		buf, ok := v.([]byte)
		if !ok {
			return errors.Errorf(`invalid value %T for %s key`, v, AuthenticatedDataKey)
		}
		m.authenticatedData = buf
	case CipherTextKey:
		buf, ok := v.([]byte)
		if !ok {
			return errors.Errorf(`invalid value %T for %s key`, v, CipherTextKey)
		}
		m.cipherText = buf
	case InitializationVectorKey:
		buf, ok := v.([]byte)
		if !ok {
			return errors.Errorf(`invalid value %T for %s key`, v, InitializationVectorKey)
		}
		m.initializationVector = buf
	case ProtectedHeadersKey:
		cv, ok := v.(Headers)
		if !ok {
			return errors.Errorf(`invalid value %T for %s key`, v, ProtectedHeadersKey)
		}
		m.protectedHeaders = cv
	case RecipientsKey:
		cv, ok := v.([]Recipient)
		if !ok {
			return errors.Errorf(`invalid value %T for %s key`, v, RecipientsKey)
		}
		m.recipients = cv
	case TagKey:
		buf, ok := v.([]byte)
		if !ok {
			return errors.Errorf(`invalid value %T for %s key`, v, TagKey)
		}
		m.tag = buf
	case UnprotectedHeadersKey:
		cv, ok := v.(Headers)
		if !ok {
			return errors.Errorf(`invalid value %T for %s key`, v, UnprotectedHeadersKey)
		}
		m.unprotectedHeaders = cv
	default:
		if m.unprotectedHeaders == nil {
			m.unprotectedHeaders = NewHeaders()
		}
		return m.unprotectedHeaders.Set(k, v)
	}
	return nil
}

type messageMarshalProxy struct {
	AuthenticatedData    string            `json:"aad,omitempty"`
	CipherText           string            `json:"ciphertext"`
	InitializationVector string            `json:"iv,omitempty"`
	ProtectedHeaders     json.RawMessage   `json:"protected"`
	Recipients           []json.RawMessage `json:"recipients,omitempty"`
	Tag                  string            `json:"tag,omitempty"`
	UnprotectedHeaders   Headers           `json:"unprotected,omitempty"`

	// For flattened structure. Headers is NOT a Headers type,
	// so that we can detect its presence by checking proxy.Headers != nil
	Headers      json.RawMessage `json:"header,omitempty"`
	EncryptedKey string          `json:"encrypted_key,omitempty"`
}

func (m *Message) MarshalJSON() ([]byte, error) {
	// This is slightly convoluted, but we need to encode the
	// protected headers, so we do it by hand
	buf := pool.GetBytesBuffer()
	defer pool.ReleaseBytesBuffer(buf)
	enc := json.NewEncoder(buf)
	fmt.Fprintf(buf, `{`)

	var wrote bool
	if aad := m.AuthenticatedData(); len(aad) > 0 {
		wrote = true
		fmt.Fprintf(buf, `%#v:`, AuthenticatedDataKey)
		if err := enc.Encode(base64.EncodeToString(aad)); err != nil {
			return nil, errors.Wrapf(err, `failed to encode %s field`, AuthenticatedDataKey)
		}
	}
	if cipherText := m.CipherText(); len(cipherText) > 0 {
		if wrote {
			fmt.Fprintf(buf, `,`)
		}
		wrote = true
		fmt.Fprintf(buf, `%#v:`, CipherTextKey)
		if err := enc.Encode(base64.EncodeToString(cipherText)); err != nil {
			return nil, errors.Wrapf(err, `failed to encode %s field`, CipherTextKey)
		}
	}

	if iv := m.InitializationVector(); len(iv) > 0 {
		if wrote {
			fmt.Fprintf(buf, `,`)
		}
		wrote = true
		fmt.Fprintf(buf, `%#v:`, InitializationVectorKey)
		if err := enc.Encode(base64.EncodeToString(iv)); err != nil {
			return nil, errors.Wrapf(err, `failed to encode %s field`, InitializationVectorKey)
		}
	}

	if h := m.ProtectedHeaders(); h != nil {
		encodedHeaders, err := h.Encode()
		if err != nil {
			return nil, errors.Wrap(err, `failed to encode protected headers`)
		}

		if len(encodedHeaders) > 2 {
			if wrote {
				fmt.Fprintf(buf, `,`)
			}
			wrote = true
			fmt.Fprintf(buf, `%#v:%#v`, ProtectedHeadersKey, string(encodedHeaders))
		}
	}

	if recipients := m.Recipients(); len(recipients) > 0 {
		if wrote {
			fmt.Fprintf(buf, `,`)
		}
		if len(recipients) == 1 { // Use flattened format
			fmt.Fprintf(buf, `%#v:`, HeadersKey)
			if err := enc.Encode(recipients[0].Headers()); err != nil {
				return nil, errors.Wrapf(err, `failed to encode %s field`, HeadersKey)
			}
			if ek := recipients[0].EncryptedKey(); len(ek) > 0 {
				fmt.Fprintf(buf, `,%#v:`, EncryptedKeyKey)
				if err := enc.Encode(base64.EncodeToString(ek)); err != nil {
					return nil, errors.Wrapf(err, `failed to encode %s field`, EncryptedKeyKey)
				}
			}
		} else {
			fmt.Fprintf(buf, `%#v:`, RecipientsKey)
			if err := enc.Encode(recipients); err != nil {
				return nil, errors.Wrapf(err, `failed to encode %s field`, RecipientsKey)
			}
		}
	}

	if tag := m.Tag(); len(tag) > 0 {
		if wrote {
			fmt.Fprintf(buf, `,`)
		}
		fmt.Fprintf(buf, `%#v:`, TagKey)
		if err := enc.Encode(base64.EncodeToString(tag)); err != nil {
			return nil, errors.Wrapf(err, `failed to encode %s field`, TagKey)
		}
	}

	if h := m.UnprotectedHeaders(); h != nil {
		unprotected, err := json.Marshal(h)
		if err != nil {
			return nil, errors.Wrap(err, `failed to encode unprotected headers`)
		}

		if len(unprotected) > 2 {
			fmt.Fprintf(buf, `,%#v:%#v`, UnprotectedHeadersKey, string(unprotected))
		}
	}
	fmt.Fprintf(buf, `}`)

	ret := make([]byte, buf.Len())
	copy(ret, buf.Bytes())
	return ret, nil
}

func (m *Message) UnmarshalJSON(buf []byte) error {
	var proxy messageMarshalProxy
	proxy.UnprotectedHeaders = NewHeaders()

	if err := json.Unmarshal(buf, &proxy); err != nil {
		return errors.Wrap(err, `failed to unmashal JSON into message`)
	}

	// Get the string value
	var protectedHeadersStr string
	if err := json.Unmarshal(proxy.ProtectedHeaders, &protectedHeadersStr); err != nil {
		return errors.Wrap(err, `failed to decode protected headers (1)`)
	}

	// It's now in _quoted_ base64 string. Decode it
	protectedHeadersRaw, err := base64.DecodeString(protectedHeadersStr)
	if err != nil {
		return errors.Wrap(err, "failed to base64 decoded protected headers buffer")
	}

	h := NewHeaders()
	if err := json.Unmarshal(protectedHeadersRaw, h); err != nil {
		return errors.Wrap(err, `failed to decode protected headers (2)`)
	}

	// if this were a flattened message, we would see a "header" and "ciphertext"
	// field. TODO: do both of these conditions need to meet, or just one?
	if proxy.Headers != nil || len(proxy.EncryptedKey) > 0 {
		recipient := NewRecipient()
		hdrs := NewHeaders()
		if err := json.Unmarshal(proxy.Headers, hdrs); err != nil {
			return errors.Wrap(err, `failed to decode headers field`)
		}

		if err := recipient.SetHeaders(hdrs); err != nil {
			return errors.Wrap(err, `failed to set new headers`)
		}

		if v := proxy.EncryptedKey; len(v) > 0 {
			buf, err := base64.DecodeString(v)
			if err != nil {
				return errors.Wrap(err, `failed to decode encrypted key`)
			}
			if err := recipient.SetEncryptedKey(buf); err != nil {
				return errors.Wrap(err, `failed to set encrypted key`)
			}
		}

		m.recipients = append(m.recipients, recipient)
	} else {
		for i, recipientbuf := range proxy.Recipients {
			recipient := NewRecipient()
			if err := json.Unmarshal(recipientbuf, recipient); err != nil {
				return errors.Wrapf(err, `failed to decode recipient at index %d`, i)
			}

			m.recipients = append(m.recipients, recipient)
		}
	}

	if src := proxy.AuthenticatedData; len(src) > 0 {
		v, err := base64.DecodeString(src)
		if err != nil {
			return errors.Wrap(err, `failed to decode "aad"`)
		}
		m.authenticatedData = v
	}

	if src := proxy.CipherText; len(src) > 0 {
		v, err := base64.DecodeString(src)
		if err != nil {
			return errors.Wrap(err, `failed to decode "ciphertext"`)
		}
		m.cipherText = v
	}

	if src := proxy.InitializationVector; len(src) > 0 {
		v, err := base64.DecodeString(src)
		if err != nil {
			return errors.Wrap(err, `failed to decode "iv"`)
		}
		m.initializationVector = v
	}

	if src := proxy.Tag; len(src) > 0 {
		v, err := base64.DecodeString(src)
		if err != nil {
			return errors.Wrap(err, `failed to decode "tag"`)
		}
		m.tag = v
	}

	m.protectedHeaders = h
	if m.storeProtectedHeaders {
		// this is later used for decryption
		m.rawProtectedHeaders = base64.Encode(protectedHeadersRaw)
	}

	if !proxy.UnprotectedHeaders.(isZeroer).isZero() {
		m.unprotectedHeaders = proxy.UnprotectedHeaders
	}

	if len(m.recipients) == 0 {
		if err := m.makeDummyRecipient(proxy.EncryptedKey, m.protectedHeaders); err != nil {
			return errors.Wrap(err, `failed to setup recipient`)
		}
	}

	return nil
}

func (m *Message) makeDummyRecipient(enckeybuf string, protected Headers) error {
	// Recipients in this case should not contain the content encryption key,
	// so move that out
	hdrs, err := protected.Clone(context.TODO())
	if err != nil {
		return errors.Wrap(err, `failed to clone headers`)
	}

	if err := hdrs.Remove(ContentEncryptionKey); err != nil {
		return errors.Wrapf(err, "failed to remove %#v from public header", ContentEncryptionKey)
	}

	enckey, err := base64.DecodeString(enckeybuf)
	if err != nil {
		return errors.Wrap(err, `failed to decode encrypted key`)
	}

	if err := m.Set(RecipientsKey, []Recipient{
		&stdRecipient{
			headers:      hdrs,
			encryptedKey: enckey,
		},
	}); err != nil {
		return errors.Wrapf(err, `failed to set %s`, RecipientsKey)
	}
	return nil
}

// Decrypt decrypts the message using the specified algorithm and key.
//
// `key` must be a private key in its "raw" format (i.e. something like
// *rsa.PrivateKey, instead of jwk.Key)
//
// This method is marked for deprecation. It will be removed from the API
// in the next major release. You should not rely on this method
// to work 100% of the time, especially when it was obtained via jwe.Parse
// instead of being constructed from scratch by this library.
func (m *Message) Decrypt(alg jwa.KeyEncryptionAlgorithm, key interface{}) ([]byte, error) {
	var ctx decryptCtx
	ctx.alg = alg
	ctx.key = key
	ctx.msg = m

	return doDecryptCtx(&ctx)
}

func doDecryptCtx(dctx *decryptCtx) ([]byte, error) {
	m := dctx.msg
	alg := dctx.alg
	key := dctx.key

	if jwkKey, ok := key.(jwk.Key); ok {
		var raw interface{}
		if err := jwkKey.Raw(&raw); err != nil {
			return nil, errors.Wrapf(err, `failed to retrieve raw key from %T`, key)
		}
		key = raw
	}

	var err error
	ctx := context.TODO()
	h, err := m.protectedHeaders.Clone(ctx)
	if err != nil {
		return nil, errors.Wrap(err, `failed to copy protected headers`)
	}
	h, err = h.Merge(ctx, m.unprotectedHeaders)
	if err != nil {
		return nil, errors.Wrap(err, "failed to merge headers for message decryption")
	}

	enc := m.protectedHeaders.ContentEncryption()
	var aad []byte
	if aadContainer := m.authenticatedData; aadContainer != nil {
		aad = base64.Encode(aadContainer)
	}

	var computedAad []byte
	if len(m.rawProtectedHeaders) > 0 {
		computedAad = m.rawProtectedHeaders
	} else {
		// this is probably not required once msg.Decrypt is deprecated
		var err error
		computedAad, err = m.protectedHeaders.Encode()
		if err != nil {
			return nil, errors.Wrap(err, "failed to encode protected headers")
		}
	}

	dec := NewDecrypter(alg, enc, key).
		AuthenticatedData(aad).
		ComputedAuthenticatedData(computedAad).
		InitializationVector(m.initializationVector).
		Tag(m.tag)

	var plaintext []byte
	var lastError error

	// if we have no recipients, pretend like we only have one
	recipients := m.recipients
	if len(recipients) == 0 {
		r := NewRecipient()
		if err := r.SetHeaders(m.protectedHeaders); err != nil {
			return nil, errors.Wrap(err, `failed to set headers to recipient`)
		}
		recipients = append(recipients, r)
	}

	for _, recipient := range recipients {
		// strategy: try each recipient. If we fail in one of the steps,
		// keep looping because there might be another key with the same algo
		if recipient.Headers().Algorithm() != alg {
			// algorithms don't match
			continue
		}

		h2, err := h.Clone(ctx)
		if err != nil {
			lastError = errors.Wrap(err, `failed to copy headers (1)`)
			continue
		}

		h2, err = h2.Merge(ctx, recipient.Headers())
		if err != nil {
			lastError = errors.Wrap(err, `failed to copy headers (2)`)
			continue
		}

		switch alg {
		case jwa.ECDH_ES, jwa.ECDH_ES_A128KW, jwa.ECDH_ES_A192KW, jwa.ECDH_ES_A256KW:
			epkif, ok := h2.Get(EphemeralPublicKeyKey)
			if !ok {
				return nil, errors.New("failed to get 'epk' field")
			}
			switch epk := epkif.(type) {
			case jwk.ECDSAPublicKey:
				var pubkey ecdsa.PublicKey
				if err := epk.Raw(&pubkey); err != nil {
					return nil, errors.Wrap(err, "failed to get public key")
				}
				dec.PublicKey(&pubkey)
			case jwk.OKPPublicKey:
				var pubkey interface{}
				if err := epk.Raw(&pubkey); err != nil {
					return nil, errors.Wrap(err, "failed to get public key")
				}
				dec.PublicKey(pubkey)
			default:
				return nil, errors.Errorf("unexpected 'epk' type %T for alg %s", epkif, alg)
			}

			if apu := h2.AgreementPartyUInfo(); len(apu) > 0 {
				dec.AgreementPartyUInfo(apu)
			}

			if apv := h2.AgreementPartyVInfo(); len(apv) > 0 {
				dec.AgreementPartyVInfo(apv)
			}
		case jwa.A128GCMKW, jwa.A192GCMKW, jwa.A256GCMKW:
			ivB64, ok := h2.Get(InitializationVectorKey)
			if !ok {
				return nil, errors.New("failed to get 'iv' field")
			}
			ivB64Str, ok := ivB64.(string)
			if !ok {
				return nil, errors.Errorf("unexpected type for 'iv': %T", ivB64)
			}
			tagB64, ok := h2.Get(TagKey)
			if !ok {
				return nil, errors.New("failed to get 'tag' field")
			}
			tagB64Str, ok := tagB64.(string)
			if !ok {
				return nil, errors.Errorf("unexpected type for 'tag': %T", tagB64)
			}
			iv, err := base64.DecodeString(ivB64Str)
			if err != nil {
				return nil, errors.Wrap(err, "failed to b64-decode 'iv'")
			}
			tag, err := base64.DecodeString(tagB64Str)
			if err != nil {
				return nil, errors.Wrap(err, "failed to b64-decode 'tag'")
			}
			dec.KeyInitializationVector(iv)
			dec.KeyTag(tag)
		case jwa.PBES2_HS256_A128KW, jwa.PBES2_HS384_A192KW, jwa.PBES2_HS512_A256KW:
			saltB64, ok := h2.Get(SaltKey)
			if !ok {
				return nil, errors.New("failed to get 'p2s' field")
			}
			saltB64Str, ok := saltB64.(string)
			if !ok {
				return nil, errors.Errorf("unexpected type for 'p2s': %T", saltB64)
			}

			count, ok := h2.Get(CountKey)
			if !ok {
				return nil, errors.New("failed to get 'p2c' field")
			}
			countFlt, ok := count.(float64)
			if !ok {
				return nil, errors.Errorf("unexpected type for 'p2c': %T", count)
			}
			salt, err := base64.DecodeString(saltB64Str)
			if err != nil {
				return nil, errors.Wrap(err, "failed to b64-decode 'salt'")
			}
			dec.KeySalt(salt)
			dec.KeyCount(int(countFlt))
		}

		plaintext, err = dec.Decrypt(recipient.EncryptedKey(), m.cipherText)
		if err != nil {
			lastError = errors.Wrap(err, `failed to decrypt`)
			continue
		}

		if h2.Compression() == jwa.Deflate {
			buf, err := uncompress(plaintext)
			if err != nil {
				lastError = errors.Wrap(err, `failed to uncompress payload`)
				continue
			}
			plaintext = buf
		}
		break
	}

	if plaintext == nil {
		if lastError != nil {
			return nil, errors.Errorf(`failed to find matching recipient to decrypt key (last error = %s)`, lastError)
		}
		return nil, errors.New("failed to find matching recipient")
	}

	return plaintext, nil
}