Refactor convergent encryption to make specifying a nonce in addition to context possible

builtin/logical/transit/backend_test.go

@@ -601,6 +601,7 @@ func TestConvergentEncryption(t *testing.T) {
 		Data: map[string]interface{}{
 			"derived":               false,
 			"convergent_encryption": true,
+			"context_as_nonce":      true,
 		},
 	}
 
@@ -619,6 +620,7 @@ func TestConvergentEncryption(t *testing.T) {
 	req.Data = map[string]interface{}{
 		"derived":               true,
 		"convergent_encryption": true,
+		"context_as_nonce":      true,
 	}
 
 	resp, err = b.HandleRequest(req)

builtin/logical/transit/lock_manager.go

@@ -105,42 +105,42 @@ func (lm *lockManager) UnlockPolicy(lock *sync.RWMutex, lockType bool) {
 // is needed (for instance, for an upgrade/migration), give up the read lock,
 // call again with an exclusive lock, then swap back out for a read lock.
 func (lm *lockManager) GetPolicyShared(storage logical.Storage, name string) (*Policy, *sync.RWMutex, error) {
-	p, lock, _, err := lm.getPolicyCommon(storage, name, false, false, false, shared)
+	p, lock, _, err := lm.getPolicyCommon(storage, name, false, false, false, false, shared)
 	if err == nil ||
 		(err != nil && err != errNeedExclusiveLock) {
 		return p, lock, err
 	}
 
 	// Try again while asking for an exlusive lock
-	p, lock, _, err = lm.getPolicyCommon(storage, name, false, false, false, exclusive)
+	p, lock, _, err = lm.getPolicyCommon(storage, name, false, false, false, false, exclusive)
 	if err != nil || p == nil || lock == nil {
 		return p, lock, err
 	}
 
 	lock.Unlock()
 
-	p, lock, _, err = lm.getPolicyCommon(storage, name, false, false, false, shared)
+	p, lock, _, err = lm.getPolicyCommon(storage, name, false, false, false, false, shared)
 	return p, lock, err
 }
 
 // Get the policy with an exclusive lock
 func (lm *lockManager) GetPolicyExclusive(storage logical.Storage, name string) (*Policy, *sync.RWMutex, error) {
-	p, lock, _, err := lm.getPolicyCommon(storage, name, false, false, false, exclusive)
+	p, lock, _, err := lm.getPolicyCommon(storage, name, false, false, false, false, exclusive)
 	return p, lock, err
 }
 
 // Get the policy with a read lock; if it returns that an exclusive lock is
 // needed, retry. If successful, call one more time to get a read lock and
 // return the value.
-func (lm *lockManager) GetPolicyUpsert(storage logical.Storage, name string, derived bool, convergent bool) (*Policy, *sync.RWMutex, bool, error) {
+func (lm *lockManager) GetPolicyUpsert(storage logical.Storage, name string, derived, convergent, contextAsNonce bool) (*Policy, *sync.RWMutex, bool, error) {
-	p, lock, _, err := lm.getPolicyCommon(storage, name, true, derived, convergent, shared)
+	p, lock, _, err := lm.getPolicyCommon(storage, name, true, derived, convergent, contextAsNonce, shared)
 	if err == nil ||
 		(err != nil && err != errNeedExclusiveLock) {
 		return p, lock, false, err
 	}
 
 	// Try again while asking for an exlusive lock
-	p, lock, upserted, err := lm.getPolicyCommon(storage, name, true, derived, convergent, exclusive)
+	p, lock, upserted, err := lm.getPolicyCommon(storage, name, true, derived, convergent, contextAsNonce, exclusive)
 	if err != nil || p == nil || lock == nil {
 		return p, lock, upserted, err
 	}
@@ -148,14 +148,14 @@ func (lm *lockManager) GetPolicyUpsert(storage logical.Storage, name string, der
 	lock.Unlock()
 
 	// Now get a shared lock for the return, but preserve the value of upsert
-	p, lock, _, err = lm.getPolicyCommon(storage, name, true, derived, convergent, shared)
+	p, lock, _, err = lm.getPolicyCommon(storage, name, true, derived, convergent, contextAsNonce, shared)
 
 	return p, lock, upserted, err
 }
 
 // When the function returns, a lock will be held on the policy if err == nil.
 // It is the caller's responsibility to unlock.
-func (lm *lockManager) getPolicyCommon(storage logical.Storage, name string, upsert, derived, convergent, lockType bool) (*Policy, *sync.RWMutex, bool, error) {
+func (lm *lockManager) getPolicyCommon(storage logical.Storage, name string, upsert, derived, convergent, contextAsNonce, lockType bool) (*Policy, *sync.RWMutex, bool, error) {
 	lock := lm.policyLock(name, lockType)
 
 	var p *Policy
@@ -204,6 +204,8 @@ func (lm *lockManager) getPolicyCommon(storage logical.Storage, name string, ups
 		if derived {
 			p.KDFMode = kdfMode
 			p.ConvergentEncryption = convergent
+			p.ContextAsNonce = new(bool)
+			*p.ContextAsNonce = contextAsNonce
 		}
 
 		err = p.rotate(storage)

builtin/logical/transit/path_datakey.go

@@ -100,7 +100,7 @@ func (b *backend) pathDatakeyWrite(
 		return nil, err
 	}
 
-	ciphertext, err := p.Encrypt(context, base64.StdEncoding.EncodeToString(newKey))
+	ciphertext, err := p.Encrypt(context, nil, base64.StdEncoding.EncodeToString(newKey))
 	if err != nil {
 		switch err.(type) {
 		case errutil.UserError:

builtin/logical/transit/path_decrypt.go

@@ -27,6 +27,11 @@ func (b *backend) pathDecrypt() *framework.Path {
 				Type:        framework.TypeString,
 				Description: "Context for key derivation. Required for derived keys.",
 			},
+
+			"nonce": &framework.FieldSchema{
+				Type:        framework.TypeString,
+				Description: "Nonce for when convergent encryption is used and the context is not used as the nonce",
+			},
 		},
 
 		Callbacks: map[logical.Operation]framework.OperationFunc{
@@ -46,17 +51,28 @@ func (b *backend) pathDecryptWrite(
 		return logical.ErrorResponse("missing ciphertext to decrypt"), logical.ErrInvalidRequest
 	}
 
+	var err error
+
 	// Decode the context if any
 	contextRaw := d.Get("context").(string)
 	var context []byte
 	if len(contextRaw) != 0 {
-		var err error
 		context, err = base64.StdEncoding.DecodeString(contextRaw)
 		if err != nil {
 			return logical.ErrorResponse("failed to decode context as base64"), logical.ErrInvalidRequest
 		}
 	}
 
+	// Decode the nonce if any
+	nonceRaw := d.Get("nonce").(string)
+	var nonce []byte
+	if len(nonceRaw) != 0 {
+		nonce, err = base64.StdEncoding.DecodeString(nonceRaw)
+		if err != nil {
+			return logical.ErrorResponse("failed to decode nonce as base64"), logical.ErrInvalidRequest
+		}
+	}
+
 	// Get the policy
 	p, lock, err := b.lm.GetPolicyShared(req.Storage, name)
 	if lock != nil {
@@ -69,7 +85,7 @@ func (b *backend) pathDecryptWrite(
 		return logical.ErrorResponse("policy not found"), logical.ErrInvalidRequest
 	}
 
-	plaintext, err := p.Decrypt(context, ciphertext)
+	plaintext, err := p.Decrypt(context, nonce, ciphertext)
 	if err != nil {
 		switch err.(type) {
 		case errutil.UserError:

builtin/logical/transit/path_encrypt.go

@@ -28,6 +28,11 @@ func (b *backend) pathEncrypt() *framework.Path {
 				Type:        framework.TypeString,
 				Description: "Context for key derivation. Required for derived keys.",
 			},
+
+			"nonce": &framework.FieldSchema{
+				Type:        framework.TypeString,
+				Description: "Nonce for when convergent encryption is used and the context is not used as the nonce",
+			},
 		},
 
 		Callbacks: map[logical.Operation]framework.OperationFunc{
@@ -63,10 +68,11 @@ func (b *backend) pathEncryptWrite(
 		return logical.ErrorResponse("missing plaintext to encrypt"), logical.ErrInvalidRequest
 	}
 
+	var err error
+
 	// Decode the context if any
 	contextRaw := d.Get("context").(string)
 	var context []byte
-	var err error
 	if len(contextRaw) != 0 {
 		context, err = base64.StdEncoding.DecodeString(contextRaw)
 		if err != nil {
@@ -74,12 +80,22 @@ func (b *backend) pathEncryptWrite(
 		}
 	}
 
+	// Decode the nonce if any
+	nonceRaw := d.Get("nonce").(string)
+	var nonce []byte
+	if len(nonceRaw) != 0 {
+		nonce, err = base64.StdEncoding.DecodeString(nonceRaw)
+		if err != nil {
+			return logical.ErrorResponse("failed to decode nonce as base64"), logical.ErrInvalidRequest
+		}
+	}
+
 	// Get the policy
 	var p *Policy
 	var lock *sync.RWMutex
 	var upserted bool
 	if req.Operation == logical.CreateOperation {
-		p, lock, upserted, err = b.lm.GetPolicyUpsert(req.Storage, name, len(context) != 0, false)
+		p, lock, upserted, err = b.lm.GetPolicyUpsert(req.Storage, name, len(context) != 0, false, false)
 	} else {
 		p, lock, err = b.lm.GetPolicyShared(req.Storage, name)
 	}
@@ -93,7 +109,7 @@ func (b *backend) pathEncryptWrite(
 		return logical.ErrorResponse("policy not found"), logical.ErrInvalidRequest
 	}
 
-	ciphertext, err := p.Encrypt(context, value)
+	ciphertext, err := p.Encrypt(context, nonce, value)
 	if err != nil {
 		switch err.(type) {
 		case errutil.UserError:

builtin/logical/transit/path_keys.go

@@ -18,22 +18,41 @@ func (b *backend) pathKeys() *framework.Path {
 			},
 
 			"derived": &framework.FieldSchema{
-				Type:        framework.TypeBool,
+				Type: framework.TypeBool,
-				Description: "Enables key derivation mode. This allows for per-transaction unique keys",
+				Description: `Enables key derivation mode. This
+allows for per-transaction unique keys.`,
 			},
 
 			"convergent_encryption": &framework.FieldSchema{
 				Type: framework.TypeBool,
-				Description: `Whether to use convergent encryption.
+				Description: `Whether to support convergent encryption.
 This is only supported when using a key with
 key derivation enabled and will require all
-context values to be 96 bits (12 bytes) when
+requests to carry both a context and 96-bit
-base64-decoded. This mode ensures that when
+(12-byte) nonce, unless the "context_as_nonce"
-the same context is supplied, the same
+feature is also enabled. The given nonce will
-ciphertext is emitted from the encryption
+be used in place of a randomly generated nonce.
-function. It is *very important* when using
+As a result, when the same context and nonce
-this mode that you ensure that all contexts
+(or context, if "context_as_nonce" is enabled)
-are *globally unique*. Failing to do so will
+are supplied, the same ciphertext is emitted
+from the encryption function. It is *very
+important* when using this mode that you ensure
+that all nonces are unique for a given context,
+or, when using "context_as_nonce", that all
+contexts are unique for a given key. Failing to
+do so will severely impact the ciphertext's
+security.`,
+			},
+
+			"context_as_nonce": &framework.FieldSchema{
+				Type: framework.TypeBool,
+				Description: `Whether to use the context value as the
+nonce in the convergent encryption operation
+mode. If set true, the user will have to
+supply a 96-bit (12-byte) context value.
+It is *very important* when using this
+mode that you ensure that all contexts are
+*globally unique*. Failing to do so will
 severely impact the security of the key.`,
 			},
 		},
@@ -54,12 +73,13 @@ func (b *backend) pathPolicyWrite(
 	name := d.Get("name").(string)
 	derived := d.Get("derived").(bool)
 	convergent := d.Get("convergent_encryption").(bool)
+	contextAsNonce := d.Get("context_as_nonce").(bool)
 
 	if !derived && convergent {
 		return logical.ErrorResponse("convergent encryption requires derivation to be enabled"), nil
 	}
 
-	p, lock, upserted, err := b.lm.GetPolicyUpsert(req.Storage, name, derived, convergent)
+	p, lock, upserted, err := b.lm.GetPolicyUpsert(req.Storage, name, derived, convergent, contextAsNonce)
 	if lock != nil {
 		defer lock.RUnlock()
 	}
@@ -107,6 +127,9 @@ func (b *backend) pathPolicyRead(
 	if p.Derived {
 		resp.Data["kdf_mode"] = p.KDFMode
 		resp.Data["convergent_encryption"] = p.ConvergentEncryption
+		if p.ContextAsNonce != nil {
+			resp.Data["context_as_nonce"] = *p.ContextAsNonce
+		}
 	}
 
 	retKeys := map[string]int64{}

builtin/logical/transit/path_rewrap.go

@@ -27,6 +27,11 @@ func (b *backend) pathRewrap() *framework.Path {
 				Type:        framework.TypeString,
 				Description: "Context for key derivation. Required for derived keys.",
 			},
+
+			"nonce": &framework.FieldSchema{
+				Type:        framework.TypeString,
+				Description: "Nonce for when convergent encryption is used and the context is not used as the nonce",
+			},
 		},
 
 		Callbacks: map[logical.Operation]framework.OperationFunc{
@@ -47,17 +52,28 @@ func (b *backend) pathRewrapWrite(
 		return logical.ErrorResponse("missing ciphertext to decrypt"), logical.ErrInvalidRequest
 	}
 
+	var err error
+
 	// Decode the context if any
 	contextRaw := d.Get("context").(string)
 	var context []byte
 	if len(contextRaw) != 0 {
-		var err error
 		context, err = base64.StdEncoding.DecodeString(contextRaw)
 		if err != nil {
 			return logical.ErrorResponse("failed to decode context as base64"), logical.ErrInvalidRequest
 		}
 	}
 
+	// Decode the nonce if any
+	nonceRaw := d.Get("nonce").(string)
+	var nonce []byte
+	if len(nonceRaw) != 0 {
+		nonce, err = base64.StdEncoding.DecodeString(nonceRaw)
+		if err != nil {
+			return logical.ErrorResponse("failed to decode nonce as base64"), logical.ErrInvalidRequest
+		}
+	}
+
 	// Get the policy
 	p, lock, err := b.lm.GetPolicyShared(req.Storage, name)
 	if lock != nil {
@@ -71,7 +87,7 @@ func (b *backend) pathRewrapWrite(
 		return logical.ErrorResponse("policy not found"), logical.ErrInvalidRequest
 	}
 
-	plaintext, err := p.Decrypt(context, value)
+	plaintext, err := p.Decrypt(context, nonce, value)
 	if err != nil {
 		switch err.(type) {
 		case errutil.UserError:
@@ -87,7 +103,7 @@ func (b *backend) pathRewrapWrite(
 		return nil, fmt.Errorf("empty plaintext returned during rewrap")
 	}
 
-	ciphertext, err := p.Encrypt(context, plaintext)
+	ciphertext, err := p.Encrypt(context, nonce, plaintext)
 	if err != nil {
 		switch err.(type) {
 		case errutil.UserError:

builtin/logical/transit/policy.go

@@ -72,6 +72,7 @@ type Policy struct {
 	Derived              bool   `json:"derived"`
 	KDFMode              string `json:"kdf_mode"`
 	ConvergentEncryption bool   `json:"convergent_encryption"`
+	ContextAsNonce       *bool  `json:"context_as_nonce"`
 
 	// The minimum version of the key allowed to be used
 	// for decryption
@@ -259,6 +260,10 @@ func (p *Policy) needsUpgrade() bool {
 		return true
 	}
 
+	if p.ConvergentEncryption && p.ContextAsNonce == nil {
+		return true
+	}
+
 	return false
 }
 
@@ -288,6 +293,14 @@ func (p *Policy) upgrade(storage logical.Storage) error {
 		persistNeeded = true
 	}
 
+	// Originally the context-as-nonce mode was the only mode, so keep that
+	// behavior if convergent encryption is already in use
+	if p.ConvergentEncryption && p.ContextAsNonce == nil {
+		p.ContextAsNonce = new(bool)
+		*p.ContextAsNonce = true
+		persistNeeded = true
+	}
+
 	if persistNeeded {
 		err := p.Persist(storage)
 		if err != nil {
@@ -307,10 +320,6 @@ func (p *Policy) DeriveKey(context []byte, ver int) ([]byte, error) {
 		return nil, errutil.InternalError{Err: "unable to access the key; no key versions found"}
 	}
 
-	if p.LatestVersion == 0 {
-		return nil, errutil.InternalError{Err: "unable to access the key; no key versions found"}
-	}
-
 	if ver <= 0 || ver > p.LatestVersion {
 		return nil, errutil.UserError{Err: "invalid key version"}
 	}
@@ -335,7 +344,7 @@ func (p *Policy) DeriveKey(context []byte, ver int) ([]byte, error) {
 	}
 }
 
-func (p *Policy) Encrypt(context []byte, value string) (string, error) {
+func (p *Policy) Encrypt(context, nonce []byte, value string) (string, error) {
 	// Decode the plaintext value
 	plaintext, err := base64.StdEncoding.DecodeString(value)
 	if err != nil {
@@ -367,15 +376,20 @@ func (p *Policy) Encrypt(context []byte, value string) (string, error) {
 		return "", errutil.InternalError{Err: err.Error()}
 	}
 
-	if p.ConvergentEncryption && len(context) != gcm.NonceSize() {
-		return "", errutil.UserError{Err: fmt.Sprintf("base64-decoded context must be %d bytes long when using convergent encryption with this key", gcm.NonceSize())}
-	}
-
-	// Compute random nonce
-	var nonce []byte
 	if p.ConvergentEncryption {
-		nonce = context
+
+		if *p.ContextAsNonce {
+			if len(context) != gcm.NonceSize() {
+				return "", errutil.UserError{Err: fmt.Sprintf("base64-decoded context must be %d bytes long when using convergent encryption with context-as-nonce with this key", gcm.NonceSize())}
+			}
+			nonce = context
+
+		} else if len(nonce) != gcm.NonceSize() {
+			return "", errutil.UserError{Err: fmt.Sprintf("base64-decoded nonce must be %d bytes long when using convergent encryption with this key", gcm.NonceSize())}
+		}
+
 	} else {
+		// Compute random nonce
 		nonce = make([]byte, gcm.NonceSize())
 		_, err = rand.Read(nonce)
 		if err != nil {
@@ -387,7 +401,10 @@ func (p *Policy) Encrypt(context []byte, value string) (string, error) {
 	out := gcm.Seal(nil, nonce, plaintext, nil)
 
 	// Place the encrypted data after the nonce
-	full := append(nonce, out...)
+	full := out
+	if !p.ConvergentEncryption {
+		full = append(nonce, out...)
+	}
 
 	// Convert to base64
 	encoded := base64.StdEncoding.EncodeToString(full)
@@ -398,12 +415,16 @@ func (p *Policy) Encrypt(context []byte, value string) (string, error) {
 	return encoded, nil
 }
 
-func (p *Policy) Decrypt(context []byte, value string) (string, error) {
+func (p *Policy) Decrypt(context, nonce []byte, value string) (string, error) {
 	// Verify the prefix
 	if !strings.HasPrefix(value, "vault:v") {
 		return "", errutil.UserError{Err: "invalid ciphertext: no prefix"}
 	}
 
+	if p.ConvergentEncryption && !*p.ContextAsNonce && (nonce == nil || len(nonce) == 0) {
+		return "", errutil.UserError{Err: "invalid convergent nonce supplied"}
+	}
+
 	splitVerCiphertext := strings.SplitN(strings.TrimPrefix(value, "vault:v"), ":", 2)
 	if len(splitVerCiphertext) != 2 {
 		return "", errutil.UserError{Err: "invalid ciphertext: wrong number of fields"}
@@ -460,8 +481,16 @@ func (p *Policy) Decrypt(context []byte, value string) (string, error) {
 	}
 
 	// Extract the nonce and ciphertext
-	nonce := decoded[:gcm.NonceSize()]
+	var ciphertext []byte
-	ciphertext := decoded[gcm.NonceSize():]
+	if p.ConvergentEncryption {
+		if *p.ContextAsNonce {
+			nonce = context
+		}
+		ciphertext = decoded
+	} else {
+		nonce = decoded[:gcm.NonceSize()]
+		ciphertext = decoded[gcm.NonceSize():]
+	}
 
 	// Verify and Decrypt
 	plain, err := gcm.Open(nil, nonce, ciphertext, nil)

builtin/logical/transit/policy_test.go

@@ -22,7 +22,7 @@ func Test_KeyUpgrade(t *testing.T) {
 
 func testKeyUpgradeCommon(t *testing.T, lm *lockManager) {
 	storage := &logical.InmemStorage{}
-	p, lock, upserted, err := lm.GetPolicyUpsert(storage, "test", false, false)
+	p, lock, upserted, err := lm.GetPolicyUpsert(storage, "test", false, false, false)
 	if lock != nil {
 		defer lock.RUnlock()
 	}
@@ -68,7 +68,7 @@ func testArchivingUpgradeCommon(t *testing.T, lm *lockManager) {
 
 	storage := &logical.InmemStorage{}
 
-	p, lock, _, err := lm.GetPolicyUpsert(storage, "test", false, false)
+	p, lock, _, err := lm.GetPolicyUpsert(storage, "test", false, false, false)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -198,7 +198,7 @@ func testArchivingCommon(t *testing.T, lm *lockManager) {
 
 	storage := &logical.InmemStorage{}
 
-	p, lock, _, err := lm.GetPolicyUpsert(storage, "test", false, false)
+	p, lock, _, err := lm.GetPolicyUpsert(storage, "test", false, false, false)
 	if lock != nil {
 		defer lock.RUnlock()
 	}