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Is AES-128-CBC secure enough to use in OpenVPN? I asked and they told me AES-128-CBC is completely broken and is considered weak encryption. Is it so?

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    AES-128-CBC is not broken but must be used correctly, nothing special just use of best practices. There was an insecure usage in TLS and it was decided that instead of fixing the usage to remove AES-CBC from use to eliminate confusion such as this. BTW, why where did you get that information, there may be more to a specific usage.
    – zaph
    Commented Jan 9, 2019 at 22:34
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    Who exactly is "they" that are telling you that AES-128-CBC is broken? Commented Jan 9, 2019 at 23:10
  • I think you read about Padding Oracle attack, this kind of attack can be applied on CBC mode operation, in that case you should use GCM, but you should include a reference to be sure.
    – hmrojas.p
    Commented Jan 9, 2019 at 23:17
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    @hmrojas.p The simple Padding Oracle solution is simply not to even check for padding errors.
    – zaph
    Commented Jan 10, 2019 at 0:37
  • @zaph well you right, the solution is a checking.
    – hmrojas.p
    Commented Jan 10, 2019 at 16:25

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As noted above, CBC mode has issues which can cause problems when used incorrectly. It's safer to use GCM. GCM provides authenticated encryption, which is generally preferred over non-authenicated encryption. This is why CBC mode was used in TLS 1.2, but was dropped for TLS 1.3.

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    OpenVPN uses CBC securely using HMAC for integrity.
    – forest
    Commented Jan 10, 2019 at 3:45

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