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S3 ETag Validator

During upload, Amazon S3 generates and assigns server-side ETag values that can be used to validate the integrity of downloaded S3 objects. s3-etv performs validation by retrieving various object attributes from the S3 API and implementing the same algorithm locally to produce an ETag value that is then compared to the server-side value.

Download binaries from the releases page.

Usage

  1. Download s3-etv from the releases page.
  2. Download the target file from AWS S3.
    • Tip: Retain the URL as it will be needed later.
  3. Run s3-etv to validate integrity of the downloaded file:
./s3-etv -u https://some-bucket.s3.amazonaws.com/some.vhd  -i ~/Downloads/some.vhd --thread-count 15
[INF] 2023/08/06 06:24:02 Retrieved ETag information via S3 API
[INF] 2023/08/06 06:24:02 ETag Value: fcd95600383564e0916872202cda9c3d-2185
[INF] 2023/08/06 06:24:02 Input File: /home/user/Downloads/some.vhd
[WRN] 2023/08/06 06:24:02 Verifying file integrity. This will take some time.
[WRN] 2023/08/06 06:24:02 Using process count: 15
[INF] 2023/08/06 06:24:04 Integrity check finished
[INF] 2023/08/06 06:24:04 AWS ETag        > fcd95600383564e0916872202cda9c3d-2185
[INF] 2023/08/06 06:24:04 Calculated ETag > fcd95600383564e0916872202cda9c3d-2185
[INF] 2023/08/06 06:24:04 ETag values matched
[INF] 2023/08/06 06:24:04 File integrity status: confirmed
[INF] 2023/08/06 06:24:04 Verification Duration: 0:0:1.1406

File integrity: verified

When the integrity check fails, File integrity: compromised is returned.

FAQ

Why is this a thing?

We get it, it isn't a very hackery tool. But we often share large files via S3 to customers to facilitate remote access during engagements and this approach provides multi-OS support with multiprocessing capabilities while avoiding garbage like PowerShell.

How does AWS S3 Generate ETags?

AWS says...