This commit adds two functions for sealing/unsealing the
etag (a.k.a. content MD5) in case of SSE single-part upload.
Sealing the ETag is neccessary in case of SSE-S3 to preserve
the security guarantees. In case of SSE-S3 AWS returns the
content-MD5 of the plaintext object as ETag. However, we
must not store the MD5 of the plaintext for encrypted objects.
Otherwise it becomes possible for an attacker to detect
equal/non-equal encrypted objects. Therefore we encrypt
the ETag before storing on the backend. But we only need
to encrypt the ETag (content-MD5) if the client send it -
otherwise the client cannot verify it anyway.
This commit adds two functions for removing
confidential information - like SSE-C keys -
from HTTP headers / object metadata.
This creates a central point grouping all
headers/entries which must be filtered / removed.
See also https://github.com/minio/minio/pull/6489#discussion_r219797993
of #6489
* crypto: add support for parsing SSE-C/SSE-S3 metadata
This commit adds support for detecting and parsing
SSE-C/SSE-S3 object metadata. With the `IsEncrypted`
functions it is possible to determine whether an object
seems to be encrypted. With the `ParseMetadata` functions
it is possible to validate such metadata and extract the
SSE-C/SSE-S3 related values.
It also fixes some naming issues.
* crypto: add functions for creating SSE object metadata
This commit adds functions for creating SSE-S3 and
SSE-C metadata. It also adds a `CreateMultipartMetadata`
for creating multipart metadata.
For all functions unit tests are included.
