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minio/cmd/encryption-v1.go

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12 KiB

/*
* Minio Cloud Storage, (C) 2017 Minio, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package cmd
import (
"bytes"
"crypto/hmac"
"crypto/md5"
"crypto/rand"
"encoding/base64"
"errors"
"io"
"net/http"
sha256 "github.com/minio/sha256-simd"
"github.com/minio/sio"
)
var (
// AWS errors for invalid SSE-C requests.
errInsecureSSERequest = errors.New("Requests specifying Server Side Encryption with Customer provided keys must be made over a secure connection")
errEncryptedObject = errors.New("The object was stored using a form of Server Side Encryption. The correct parameters must be provided to retrieve the object")
errInvalidSSEAlgorithm = errors.New("Requests specifying Server Side Encryption with Customer provided keys must provide a valid encryption algorithm")
errMissingSSEKey = errors.New("Requests specifying Server Side Encryption with Customer provided keys must provide an appropriate secret key")
errInvalidSSEKey = errors.New("The secret key was invalid for the specified algorithm")
errMissingSSEKeyMD5 = errors.New("Requests specifying Server Side Encryption with Customer provided keys must provide the client calculated MD5 of the secret key")
errSSEKeyMD5Mismatch = errors.New("The calculated MD5 hash of the key did not match the hash that was provided")
errSSEKeyMismatch = errors.New("The client provided key does not match the key provided when the object was encrypted") // this msg is not shown to the client
// Additional Minio errors for SSE-C requests.
errObjectTampered = errors.New("The requested object was modified and may be compromised")
)
const (
// SSECustomerAlgorithm is the AWS SSE-C algorithm HTTP header key.
SSECustomerAlgorithm = "X-Amz-Server-Side-Encryption-Customer-Algorithm"
// SSECustomerKey is the AWS SSE-C encryption key HTTP header key.
SSECustomerKey = "X-Amz-Server-Side-Encryption-Customer-Key"
// SSECustomerKeyMD5 is the AWS SSE-C encryption key MD5 HTTP header key.
SSECustomerKeyMD5 = "X-Amz-Server-Side-Encryption-Customer-Key-MD5"
)
const (
// SSECustomerKeySize is the size of valid client provided encryption keys in bytes.
// Currently AWS supports only AES256. So the SSE-C key size is fixed to 32 bytes.
SSECustomerKeySize = 32
// SSECustomerAlgorithmAES256 the only valid S3 SSE-C encryption algorithm identifier.
SSECustomerAlgorithmAES256 = "AES256"
)
// SSE-C key derivation:
// H: Hash function, M: MAC function
//
// key := 32 bytes # client provided key
// r := H(random(32 bytes)) # saved as object metadata [ServerSideEncryptionIV]
// key_mac := M(H(key), r) # saved as object metadata [ServerSideEncryptionKeyMAC]
// enc_key := M(key, key_mac)
//
//
// SSE-C key verification:
// H: Hash function, M: MAC function
//
// key := 32 bytes # client provided key
// r := object metadata [ServerSideEncryptionIV]
// key_mac := object metadata [ServerSideEncryptionKeyMAC]
// key_mac' := M(H(key), r)
//
// check: key_mac != key_mac' => fail with invalid key
//
// enc_key := M(key, key_mac')
const (
// ServerSideEncryptionIV is a 32 byte randomly generated IV used to derive an
// unique encryption key from the client provided key. The combination of this value
// and the client-provided key must be unique to provide the DARE tamper-proof property.
ServerSideEncryptionIV = ReservedMetadataPrefix + "Server-Side-Encryption-Iv"
// ServerSideEncryptionKDF is the combination of a hash and MAC function used to derive
// the SSE-C encryption key from the user-provided key.
ServerSideEncryptionKDF = ReservedMetadataPrefix + "Server-Side-Encryption-Kdf"
// ServerSideEncryptionKeyMAC is the MAC of the hash of the client-provided key and the
// X-Minio-Server-Side-Encryption-Iv. This value must be used to verify that the client
// provided the correct key to follow S3 spec.
ServerSideEncryptionKeyMAC = ReservedMetadataPrefix + "Server-Side-Encryption-Key-Mac"
)
// SSEKeyDerivationHmacSha256 specifies SHA-256 as hash function and HMAC-SHA256 as MAC function
// as the functions used to derive the SSE-C encryption keys from the client-provided key.
const SSEKeyDerivationHmacSha256 = "HMAC-SHA256"
// IsSSECustomerRequest returns true if the given HTTP header
// contains server-side-encryption with customer provided key fields.
func IsSSECustomerRequest(header http.Header) bool {
return header.Get(SSECustomerAlgorithm) != "" || header.Get(SSECustomerKey) != "" || header.Get(SSECustomerKeyMD5) != ""
}
// ParseSSECustomerRequest parses the SSE-C header fields of the provided request.
// It returns the client provided key on success.
func ParseSSECustomerRequest(r *http.Request) (key []byte, err error) {
if !globalIsSSL { // minio only supports HTTP or HTTPS requests not both at the same time
// we cannot use r.TLS == nil here because Go's http implementation reflects on
// the net.Conn and sets the TLS field of http.Request only if it's an tls.Conn.
// Minio uses a BufConn (wrapping a tls.Conn) so the type check within the http package
// will always fail -> r.TLS is always nil even for TLS requests.
return nil, errInsecureSSERequest
}
header := r.Header
if algorithm := header.Get(SSECustomerAlgorithm); algorithm != SSECustomerAlgorithmAES256 {
return nil, errInvalidSSEAlgorithm
}
if header.Get(SSECustomerKey) == "" {
return nil, errMissingSSEKey
}
if header.Get(SSECustomerKeyMD5) == "" {
return nil, errMissingSSEKeyMD5
}
key, err = base64.StdEncoding.DecodeString(header.Get(SSECustomerKey))
if err != nil {
return nil, errInvalidSSEKey
}
header.Del(SSECustomerKey) // make sure we do not save the key by accident
if len(key) != SSECustomerKeySize {
return nil, errInvalidSSEKey
}
keyMD5, err := base64.StdEncoding.DecodeString(header.Get(SSECustomerKeyMD5))
if err != nil {
return nil, errSSEKeyMD5Mismatch
}
if md5Sum := md5.Sum(key); !bytes.Equal(md5Sum[:], keyMD5) {
return nil, errSSEKeyMD5Mismatch
}
return key, nil
}
// EncryptRequest takes the client provided content and encrypts the data
// with the client provided key. It also marks the object as client-side-encrypted
// and sets the correct headers.
func EncryptRequest(content io.Reader, r *http.Request, metadata map[string]string) (io.Reader, error) {
key, err := ParseSSECustomerRequest(r)
if err != nil {
return nil, err
}
delete(metadata, SSECustomerKey) // make sure we do not save the key by accident
// security notice:
// Reusing a tuple (nonce, client provided key) will produce the same encryption key
// twice and breaks the tamper-proof property. However objects are still confidential.
// Therefore the nonce must be unique but need not to be undistinguishable from true
// randomness.
nonce := make([]byte, 32) // generate random nonce to derive encryption key
if _, err = io.ReadFull(rand.Reader, nonce); err != nil {
return nil, err
}
iv := sha256.Sum256(nonce) // hash output to not reveal any stat. weaknesses of the PRNG
keyHash := sha256.Sum256(key) // derive MAC of the client-provided key
mac := hmac.New(sha256.New, keyHash[:])
mac.Write(iv[:])
keyMAC := mac.Sum(nil)
mac = hmac.New(sha256.New, key) // derive encryption key
mac.Write(keyMAC)
reader, err := sio.EncryptReader(content, sio.Config{Key: mac.Sum(nil)})
if err != nil {
return nil, errInvalidSSEKey
}
metadata[ServerSideEncryptionIV] = base64.StdEncoding.EncodeToString(iv[:])
metadata[ServerSideEncryptionKDF] = SSEKeyDerivationHmacSha256
metadata[ServerSideEncryptionKeyMAC] = base64.StdEncoding.EncodeToString(keyMAC)
return reader, nil
}
// DecryptRequest decrypts the object with the client provided key. It also removes
// the client-side-encryption metadata from the object and sets the correct headers.
func DecryptRequest(client io.Writer, r *http.Request, metadata map[string]string) (io.WriteCloser, error) {
key, err := ParseSSECustomerRequest(r)
if err != nil {
return nil, err
}
delete(metadata, SSECustomerKey) // make sure we do not save the key by accident
if metadata[ServerSideEncryptionKDF] != SSEKeyDerivationHmacSha256 { // currently HMAC-SHA256 is the only option
return nil, errObjectTampered
}
nonce, err := base64.StdEncoding.DecodeString(metadata[ServerSideEncryptionIV])
if err != nil || len(nonce) != 32 {
return nil, errObjectTampered
}
keyMAC, err := base64.StdEncoding.DecodeString(metadata[ServerSideEncryptionKeyMAC])
if err != nil || len(keyMAC) != 32 {
return nil, errObjectTampered
}
keyHash := sha256.Sum256(key) // verify that client provided correct key
mac := hmac.New(sha256.New, keyHash[:])
mac.Write(nonce)
if !hmac.Equal(keyMAC, mac.Sum(nil)) {
return nil, errSSEKeyMismatch // client-provided key is wrong or object metadata was modified
}
mac = hmac.New(sha256.New, key) // derive decryption key
mac.Write(keyMAC)
writer, err := sio.DecryptWriter(client, sio.Config{Key: mac.Sum(nil)})
if err != nil {
return nil, errInvalidSSEKey
}
delete(metadata, ServerSideEncryptionIV)
delete(metadata, ServerSideEncryptionKDF)
delete(metadata, ServerSideEncryptionKeyMAC)
return writer, nil
}
// IsEncrypted returns true if the object is marked as encrypted.
func (o *ObjectInfo) IsEncrypted() bool {
if _, ok := o.UserDefined[ServerSideEncryptionIV]; ok {
return true
}
if _, ok := o.UserDefined[ServerSideEncryptionKDF]; ok {
return true
}
if _, ok := o.UserDefined[ServerSideEncryptionKeyMAC]; ok {
return true
}
return false
}
// DecryptedSize returns the size of the object after decryption in bytes.
// It returns an error if the object is not encrypted or marked as encrypted
// but has an invalid size.
// DecryptedSize panics if the referred object is not encrypted.
func (o *ObjectInfo) DecryptedSize() (int64, error) {
if !o.IsEncrypted() {
panic("cannot compute decrypted size of an object which is not encrypted")
}
if o.Size == 0 {
return o.Size, nil
}
size := (o.Size / (32 + 64*1024)) * (64 * 1024)
if mod := o.Size % (32 + 64*1024); mod > 0 {
if mod < 33 {
return -1, errObjectTampered // object is not 0 size but smaller than the smallest valid encrypted object
}
size += mod - 32
}
return size, nil
}
// EncryptedSize returns the size of the object after encryption.
// An encrypted object is always larger than a plain object
// except for zero size objects.
func (o *ObjectInfo) EncryptedSize() int64 {
size := (o.Size / (64 * 1024)) * (32 + 64*1024)
if mod := o.Size % (64 * 1024); mod > 0 {
size += mod + 32
}
return size
}
// DecryptObjectInfo tries to decrypt the provided object if it is encrypted.
// It fails if the object is encrypted and the HTTP headers don't contain
// SSE-C headers or the object is not encrypted but SSE-C headers are provided. (AWS behavior)
// DecryptObjectInfo returns 'ErrNone' if the object is not encrypted or the
// decryption succeeded.
//
// DecryptObjectInfo also returns whether the object is encrypted or not.
func DecryptObjectInfo(info *ObjectInfo, headers http.Header) (apiErr APIErrorCode, encrypted bool) {
if apiErr, encrypted = ErrNone, info.IsEncrypted(); !encrypted && IsSSECustomerRequest(headers) {
apiErr = ErrInvalidEncryptionParameters
} else if encrypted {
if !IsSSECustomerRequest(headers) {
apiErr = ErrSSEEncryptedObject
return
}
var err error
if info.Size, err = info.DecryptedSize(); err != nil {
apiErr = toAPIErrorCode(err)
}
}
return
}