This looks like it is the same problem you had here.
It looks like you are behind a proxy that is making a mess of your SSL certificates.
Can you check what certificate your web browser is using for our download site?
If you are using Google Chrome with Dev Tools enabled, the steps to do that are:
(1) Open https://artifacts.elastic.co/maven in Chrome
(2) Right click on the page and select Inspect
(3) In the Dev Tools window, click the Security tab
(4) Click the View certificate button
(5) The certificate should say:
*.elastic.co
Issued by: DigiCert SHA2 Secure Server CA
(6) Expand the > Details section in that same popup, and then scroll to the very bottom
(7) The fingerprints for the certificate should be:
SHA-256: 8 2E 31 1B D2 9C DF E4 18 78 C6 17 D5 CA E7
SHA-1: FB C0 C2 71 9F 00 59 21 71 DF 50 DB A1 DF FD B8 56 21 D1 8F
If those details don't match what you see in your browser, then something in your corporate environment is causing your download problem and you'll need to discuss it with your internal network administrators.