This commit adds two new functions to the
internal `etag` package:
- `ETag.Format`
- `Decrypt`
The `Decrypt` function decrypts an encrypted
ETag using a decryption key. It returns not
encrypted / multipart ETags unmodified.
The `Decrypt` function is mainly used when
handling SSE-S3 encrypted single-part objects.
In particular, the ETag of an SSE-S3 encrypted
single-part object needs to be decrypted since
S3 clients expect that this ETag is equal to the
content MD5.
The `ETag.Format` method also covers SSE ETag handling.
MinIO encrypts all ETags of SSE single part objects.
However, only the ETag of SSE-S3 encrypted single part
objects needs to be decrypted.
The ETag of an SSE-C or SSE-KMS single part object
does not correspond to its content MD5 and can be
a random value.
The `ETag.Format` function formats an ETag such that
it is an AWS S3 compliant ETag. In particular, it
returns non-encrypted ETags (single / multipart)
unmodified. However, for encrypted ETags it returns
the trailing 16 bytes as ETag. For encrypted ETags
the last 16 bytes will be a random value.
The main purpose of `Format` is to format ETags
such that clients accept them as well-formed AWS S3
ETags.
It differs from the `String` method since `String`
will return string representations for encrypted
ETags that are not AWS S3 compliant.
Signed-off-by: Andreas Auernhammer <hi@aead.dev>
This commit fixes a subtle bug in the ETag
`IsEncrypted` implementation.
An encrypted ETag may contain random bytes,
i.e. some randomness used for encryption.
This random value can contain a '-' byte
simple due to being randomly generated.
Before, the `IsEncrypted` implementation
incorrectly assumed that an encrypted ETag
cannot contain a '-' since it would be a
multipart ETag. Multipart ETags have a
16 byte value followed by a '-' and the part number.
For example:
```
059ba80b807c3c776fb3bcf3f33e11ae-2
```
However, the following encrypted ETag
```
20000f00db2d90a7b40782d4cff2b41a7799fc1e7ead25972db65150118dfbe2ba76a3c002da28f85c840cd2001a28a9
```
also contains a '-' byte but is not a multipart ETag.
This commit fixes the `IsEncrypted` implementation
simply by checking whether the ETag is at least 32
bytes long. A valid multipart ETag is never 32 bytes
long since a part number must be <= 10000.
However, an encrypted ETag must be at least 32 bytes
long. It contains the encrypted ETag bytes (16 bytes)
and the authentication tag added by the AEAD cipher (again
16 bytes).
Signed-off-by: Andreas Auernhammer <hi@aead.dev>
This is to ensure that there are no projects
that try to import `minio/minio/pkg` into
their own repo. Any such common packages should
go to `https://github.com/minio/pkg`
Andreas Auernhammer
Harshavardhana