Issuer: C=US, O=Apple Inc., OU=Apple Worldwide Developer Relations, CN=Apple Worldwide Developer Relations Certification Authority
Validity
Not Before: Nov 11 21:58:01 2010 GMT
Not After : Nov 11 21:58:01 2015 GMT
Subject: CN=Mac App Store Receipt Signing, OU=Apple Worldwide Developer Relations, O=Apple Inc., C=US
A reboot did indeed fix it for me. It asked me to sign back in to the app store, said it was verifying the app, and then updated the certificate chain:
$ openssl pkcs7 -inform der -in /Applications/1Password.app/Contents/_MASReceipt/receipt -print_certs -text
Certificate:
Data:
Version: 3 (0x2)
Serial Number:
52:a4:b9:c5:e1:b1:18:81
Signature Algorithm: sha256WithRSAEncryption
Issuer: C=US, O=Apple Inc., OU=Apple Worldwide Developer Relations, CN=Apple Worldwide Developer Relations Certification Authority
Validity
Not Before: Sep 24 19:09:31 2015 GMT
Not After : Oct 23 19:09:31 2017 GMT
Subject: CN=Mac App Store and iTunes Store Receipt Signing, OU=Apple Worldwide Developer Relations, O=Apple Inc., C=US