In Version 7.0, the Crypto.cs (.vb) file is located in the \App_Code\Data Access Layer\Shared folder.
During migration, Crypto.cs (.vb) is removed from the \App_Code\Shared folder and a new version is copied to the \App_Code\Data Access Layer\Shared folder. The new version has namespace <App Namespace>.Data instead of <App Namespace>.Business where <App Namespace> is your application namespace.
After migration, re-apply any customizations you may have made to the original Crypto.cs (.vb). Also, make sure these declarations are added to the files referring to the Crypto classes
Crypto.cs:
using <App Namespace >.Data
Crypto.vb:
Imports < App Namespace >.Data
Version 7.0 Application Migration