Verifying a Signed Export

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It is possible to digitally sign an export of archived messages to the file system if the EML or MSG format is used. This helps to ensure the integrity of each exported email while it resides outside of the archive. A SHA256 hash of the public key that can be used to verify the signatures is stored in the archive's tamper proof audit log.

Prerequisites

To verify the integrity of a signed export, the use of OpenSSL or LibreSSL is recommended. Follow the instructions below, if OpenSSL or LibreSSL is not yet installed on the computer where the verification should take place.

Linux or MacOS

Use the built-in package management to install the latest version of OpenSSL or LibreSSL.

Windows

The LibreSSL project provides Windows binaries. Download the most recent available version from https://www.libressl.org and extract it to your local disk.

It is recommended to add the location containing the the openssl.exe executable to your system's PATH variable. Otherwise update the PATH variable for a running PowerShell instance with the following command prior to executing the commands below:

  env:Path += ";C:\PATH_TO_OPENSSL_EXECUTABLE"

Create Hash of Public Key

The following command generates a SHA256 hash of the public key in order to verify it against the hash recorded in MailStore's Audit Log.

  openssl dgst -sha256 -hex publickey.pem

Verify All Emails

The following one-liners can be used to verify a signed export including all subdirectories. The commands are to be executed inside the export's target directory.

Linux or MacOS

  find . -name '*.eml' -exec openssl dgst -sha256 -verify publickey.pem -signature \{}.sig \{} \;

Windows (PowerShell)

  ls -r *.eml | ForEach-Object { $file_sig = ($_.FullName) + '.sig';  $file_eml = $_.FullName; Write-Host -NoNewLine ($_.Basename) `t": " ; openssl.exe dgst -sha256 -verify publickey.pem -signature  "$file_sig" "$file_eml" }
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  • For private use there is a free tool for email archiving furthermore: MailStore Home.