visual studio 2015 - Passwords not working after having to change machine key for VS2015 upgrade -

i'm trying convert vs2010 web site vs2015 web application (c#). latest issue i've run vs2015 requires sha1 or hmacsha256,384,512. old site, , used 3des. uses .net 2.0 membership encrypted passwords. i've read says .net membership uses machine key encryption when has encrypted passwords. know need switch hashed passwords, , on list of items do.

when using <machinekey compatibilitymode="framework45" /> or machinekey.protect ,   machinekey.unprotect apis, 'validation' attribute must 1 of these values:   sha1, hmacsha256, hmacsha384, hmacsha512, or alg:[keyedhashalgorithm] 

the issue can't seem login after has changed. assume it's because validation using different algorithm, , no match found.

is there anyway retain validation without having decrypt every password , hash or reencrypt it? or should convert passwords hashed avoid this? or there option?

ok. turns out there compatibility mode seems work , allow me not change encryption. have add compatibilitymode="framework20sp2" machinekey in web.config follows:

<machinekey compatibilitymode="framework20sp2" validationkey="..."     decryptionkey="..." validation="3des" /> 

hope helps else runs this.