CA trust is important. See what @Gil asked about that earlier on the thread and 
my reply.

Charles


-----Original Message-----
From: IBM Mainframe Discussion List [mailto:IBM-MAIN@LISTSERV.UA.EDU] On Behalf 
Of Pew, Curtis G
Sent: Friday, April 6, 2018 9:44 AM
To: IBM-MAIN@LISTSERV.UA.EDU
Subject: Re: Software Delivery on Tape to be Discontinued


> On Apr 6, 2018, at 7:57 AM, Charles Mills <charl...@mcn.org> wrote:
> 
> Your certificate contains the public half of a public-private key pair. You 
> generated that pair and keep the private part private.
> 
> The entire certificate is signed by a certificate authority. In other words, 
> it contains a hash encrypted with the private key of the CA.
> 
> The recipient of the certificate verifies that it is valid by verifying that 
> the hash can be decrypted with the CA's public key, which is contained in the 
> recipient's CA certificate.
> 
> So ... your private key has played no part in validating the certificate.
> 
> Now ... for data traffic purposes, the recipient creates a random number 
> which will be used for secret key encryption/decryption of data traffic. He 
> encrypts that random number with the public key from the certificate and 
> sends it to you. You decrypt it with your private key and use it for secret 
> key encryption/decryption of session traffic. That is where your private key 
> comes in.
> 
> The above is a simplification and leaves out details like client certificates 
> and intermediate certificates, but it accurately represents the essence of 
> the thing.

Just to play devil’s advocate here, though:

• How do you know if you can trust the CA? How carefully do they vet the source 
of the public key before they sign it? How carefully do they secure their 
private key?

• For that matter, how carefully has the person you’re communicating with 
secured his private key?

At some point you have to trust someone, but if you’re super paranoid (as 
seemed to be the case in the post that started this discussion) you’ll want to 
limit how many people you trust, and you’ll want to continually verify that 
your trust is warranted. I can conceive of cases where you’d want to begin by 
asking your partner to hand deliver his public key, and provide strong 
guarantees about his policies for securing the corresponding private key.


-- 
Pew, Curtis G
curtis....@austin.utexas.edu
ITS Systems/Core/Administrative Services


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