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b181a693fb
This commit fixes a weakness of the key-encryption-key derivation for SSE-C encrypted objects. Before this change the key-encryption-key was not bound to / didn't depend on the object path. This allows an attacker to repalce objects - encrypted with the same client-key - with each other. This change fixes this issue by updating the key-encryption-key derivation to include: - the domain (in this case SSE-C) - a canonical object path representation - the encryption & key derivation algorithm Changing the object path now causes the KDF to derive a different key-encryption-key such that the object-key unsealing fails. Including the domain (SSE-C) and encryption & key derivation algorithm is not directly neccessary for this fix. However, both will be included for the SSE-S3 KDF. So they are included here to avoid updating the KDF again when we add SSE-S3. The leagcy KDF 'DARE-SHA256' is only used for existing objects and never for new objects / key rotation.
116 lines
5 KiB
Go
116 lines
5 KiB
Go
// Minio Cloud Storage, (C) 2015, 2016, 2017, 2018 Minio, Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// Package crypto implements AWS S3 related cryptographic building blocks
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// for implementing Server-Side-Encryption (SSE-S3) and Server-Side-Encryption
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// with customer provided keys (SSE-C).
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//
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// All objects are encrypted with an unique and randomly generated 'ObjectKey'.
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// The ObjectKey itself is never stored in plaintext. Instead it is only stored
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// in a sealed from. The sealed 'ObjectKey' is created by encrypting the 'ObjectKey'
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// with an unique key-encryption-key. Given the correct key-encryption-key the
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// sealed 'ObjectKey' can be unsealed and the object can be decrypted.
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//
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//
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// ## SSE-C
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//
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// SSE-C computes the key-encryption-key from the client-provided key, an
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// initialization vector (IV) and the bucket/object path.
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//
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// 1. Encrypt:
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// Input: ClientKey, bucket, object, metadata, object_data
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// - IV := Random({0,1}²⁵⁶)
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// - ObjectKey := SHA256(ClientKey || Random({0,1}²⁵⁶))
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// - KeyEncKey := HMAC-SHA256(ClientKey, IV || 'SSE-C' || 'DAREv2-HMAC-SHA256' || bucket || '/' || object)
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// - SealedKey := DAREv2_Enc(KeyEncKey, ObjectKey)
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// - enc_object_data := DAREv2_Enc(ObjectKey, object_data)
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// - metadata <- IV
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// - metadata <- SealedKey
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// Output: enc_object_data, metadata
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//
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// 2. Decrypt:
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// Input: ClientKey, bucket, object, metadata, enc_object_data
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// - IV <- metadata
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// - SealedKey <- metadata
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// - KeyEncKey := HMAC-SHA256(ClientKey, IV || 'SSE-C' || 'DAREv2-HMAC-SHA256' || bucket || '/' || object)
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// - ObjectKey := DAREv2_Dec(KeyEncKey, SealedKey)
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// - object_data := DAREv2_Dec(ObjectKey, enc_object_data)
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// Output: object_data
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//
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//
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// ## SSE-S3
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//
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// SSE-S3 can use either a master key or a KMS as root-of-trust.
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// The en/decryption slightly depens upon which root-of-trust is used.
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//
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// ### SSE-S3 and single master key
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//
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// The master key is used to derive unique object- and key-encryption-keys.
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// SSE-S3 with a single master key works as SSE-C where the master key is
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// used as the client-provided key.
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//
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// 1. Encrypt:
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// Input: MasterKey, bucket, object, metadata, object_data
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// - IV := Random({0,1}²⁵⁶)
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// - ObjectKey := SHA256(MasterKey || Random({0,1}²⁵⁶))
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// - KeyEncKey := HMAC-SHA256(MasterKey, IV || 'SSE-S3' || 'DAREv2-HMAC-SHA256' || bucket || '/' || object)
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// - SealedKey := DAREv2_Enc(KeyEncKey, ObjectKey)
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// - enc_object_data := DAREv2_Enc(ObjectKey, object_data)
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// - metadata <- IV
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// - metadata <- SealedKey
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// Output: enc_object_data, metadata
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//
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// 2. Decrypt:
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// Input: MasterKey, bucket, object, metadata, enc_object_data
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// - IV <- metadata
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// - SealedKey <- metadata
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// - KeyEncKey := HMAC-SHA256(MasterKey, IV || 'SSE-S3' || 'DAREv2-HMAC-SHA256' || bucket || '/' || object)
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// - ObjectKey := DAREv2_Dec(KeyEncKey, SealedKey)
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// - object_data := DAREv2_Dec(ObjectKey, enc_object_data)
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// Output: object_data
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//
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//
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// ### SSE-S3 and KMS
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//
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// SSE-S3 requires that the KMS provides two functions:
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// 1. Generate(KeyID) -> (Key, EncKey)
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// 2. Unseal(KeyID, EncKey) -> Key
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//
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// 1. Encrypt:
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// Input: KeyID, bucket, object, metadata, object_data
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// - Key, EncKey := Generate(KeyID)
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// - IV := Random({0,1}²⁵⁶)
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// - ObjectKey := SHA256(Key, Random({0,1}²⁵⁶))
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// - KeyEncKey := HMAC-SHA256(Key, IV || 'SSE-S3' || 'DAREv2-HMAC-SHA256' || bucket || '/' || object)
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// - SealedKey := DAREv2_Enc(KeyEncKey, ObjectKey)
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// - enc_object_data := DAREv2_Enc(ObjectKey, object_data)
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// - metadata <- IV
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// - metadata <- KeyID
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// - metadata <- EncKey
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// - metadata <- SealedKey
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// Output: enc_object_data, metadata
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//
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// 2. Decrypt:
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// Input: bucket, object, metadata, enc_object_data
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// - KeyID <- metadata
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// - EncKey <- metadata
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// - IV <- metadata
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// - SealedKey <- metadata
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// - Key := Unseal(KeyID, EncKey)
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// - KeyEncKey := HMAC-SHA256(Key, IV || 'SSE-S3' || 'DAREv2-HMAC-SHA256' || bucket || '/' || object)
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// - ObjectKey := DAREv2_Dec(KeyEncKey, SealedKey)
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// - object_data := DAREv2_Dec(ObjectKey, enc_object_data)
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// Output: object_data
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//
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package crypto
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