This has always worked for me.

http://blogs.msdn.com/b/mattm/archive/2012/03/23/ssis-catalog-backup-and-restore.aspx

USE SSISDB
BACKUP MASTER KEY TO FILE = 'c:\DMK\SSISDB\key'
ENCRYPTION BY PASSWORD = 'OLDKEY'

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USE SSISDB
RESTORE MASTER KEY FROM FILE = 'D:\MasterKeyBackup\SSIS-Server1234\key'
DECRYPTION BY PASSWORD = 'OLDKEY'
ENCRYPTION BY PASSWORD = 'NewKEY'
FORCE

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USE master
GO
ALTER DATABASE SSISDB SET TRUSTWORTHY ON

Make sure is_trustworthy is set to ON in the restored database otherwise packages will not execute.