Get subscriber's name from SSRS database - sql-server

Question

what I am trying to do is creating a report about failed subscriptions in MS SQL Server Report Server (SSRS). What I have done so far is the following SQL statement:
USE ReportServer
GO
WITH SubscriptionsCTE AS
(
SELECT
c.[Name],
c.[Path],
s.[Description],
s.LastStatus,
s.LastRunTime,
CONVERT(xml, s.ExtensionSettings) AS ExtensionSettings,
s.DeliveryExtension
FROM
dbo.Subscriptions s
INNER JOIN dbo.[Catalog] c ON c.ItemID = s.Report_OID
WHERE
s.LastStatus LIKE 'Failure%'
)
SELECT
[Name],
[Path],
[Description],
LastStatus,
LastRuntime,
CASE
WHEN DeliveryExtension = 'Report Server FileShare' THEN (SELECT e.c.value('(Value/text())[1]', 'nvarchar(max)') FROM ExtensionSettings.nodes('ParameterValues/ParameterValue') e(c) WHERE e.c.value('(Name/text())[1]', 'nvarchar(max)') = 'USERNAME')
WHEN DeliveryExtension = 'Report Server Email' THEN (SELECT e.c.value('(Value/text())[1]', 'nvarchar(max)') FROM ExtensionSettings.nodes('ParameterValues/ParameterValue') e(c) WHERE e.c.value('(Name/text())[1]', 'nvarchar(max)') = 'TO')
ELSE NULL
END AS Subscriber
FROM
SubscriptionsCTE
The problem is that the field Subscriber is encrypted for FileShare subscriptions. I understand that it is for the password... but for the user name? As an administrator I have access to the subscriptions via the GUI, but it is a pain to look into every report's admin panel to find out the user name.
I did something like
CASE WHEN Subscriber = '(some encrypted string)' THEN 'User 1'
WHEN Subscriber = '(some other encrypted string)' THEN 'User 2'
(etc.)
ELSE NULL
END AS Subscriber
But obviously, it is not encrypted in the same way in every record, so 'User 1' has a different encrypted string in every subscription.
Is there any way to decrypt these strings? I have the .snk file from the Report Server certificates backup (and know the password for it). Does this help?
Thanks for helping...
Best wishes
Michael