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Attach whole certificate chain when signing e-mails using S/MIME

Hello,


I'd like to sign e-mails using S/MIME and the iOS mail app.


Therefore I installed the certificate containing my private key (issued by certum.eu) as a profile and activated S/MIME in the mail account settings (iOS settings). The certificate is selected there properly and the option to sign e-mails automatically has been enabled.


When I send e-mails now, they get signed - but not correctly: some e-mail clients say the signature was invalid.


When I send and sign e-mails with Outlook for Windows using the same certificate all the e-mail clients recognize the signature as valid.


The problem seems to be that the iOS mail app does not attach the whole certificate chain to the signature. Some e-mail client thus cannot validate it. (Windows for example is enrolled with certum's root CA by default but without the required intermediate certificates.)


The certificate I imported into iOS DOES contain all intermediate certificates (and they are listed in iOS when I retrieve the certificate's details there) and iOS says the certificate is 'trustworthy'. So all information needed should be available on the device.


How can I make the mail app behave like Outlook? Thank you very much in advance.


Best wishes

iPhone 5s, iOS 8.3

Posted on Apr 29, 2015 2:21 AM

Reply
1 reply

Apr 30, 2015 9:10 AM in response to tque

Hello,


I verified my assumption using the openssl pkcs7 -print_certs command.


smime.p7s files generated by Outlook for Windows do contain three -----BEGIN CERTIFICATE----- parts (one for each certificate in the chain) while those signature files generated by Apple iOS Mail contain my personal certificate only.


I have imported the same key file (.pfx) to Outlook (on five Windows computers) and iOS. Why does iOS Mail behave so differently?

Attach whole certificate chain when signing e-mails using S/MIME

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