I’ve seen some conflicting processes out there, here’s what worked for me in May, 2020:
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Download and install DB Browser for SQLitebut note that YOU MUST download the version specifically built withSQLCiphersupport. This version is not obviously available on their website, but you can find it in the nightly build folder hereWhen I tried to open the database with the default version of DB Browserit asked for a key or passphrase but it was never successful in decrypting the database. (This was what you might call infuriating)You can find those builds here: nightlies.sqlitebrowser.org/latest 
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Open the folder in Finder by pressing Shift + Command ⌘ + g (or open the Windowmenu and clickGo to Folder) and enter the following path:/Users/{USERNAME}/Library/Application Support/Signal
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Open the file config.jsonin your favorite text editor and copy the value of key, for if you saw the following you would copyA_VERY_LONG_STRING_OF_LETTERS_AND_NUMBERSwithout the quotation marks.{ "window": null, "key": "A_VERY_LONG_STRING_OF_LETTERS_AND_NUMBERS", "mediaPermissions": true }
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Back in Finder open the folder sql
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Open the file db.sqlite(by right clicking on the file and pressingopen as, dragging the database to the application, etc.) in your newly installed version of DB Browser for SQLite.
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Switch the decryption method from passphrasetoraw keyin the dropdown menu
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Ensure that SQLCipher 4 Defaultsis checked.SQLCipher 3 Defaultsdid not work for me.
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Type 0xin thepasswordbox and then paste the key you copied fromconfig.json.
- With our previous example you would enter 0xA_VERY_LONG_STRING_OF_LETTERS_AND_NUMBERS
- Press OK
You should be in, the rest is up to you!