[SSH] Added key size selection

[axmanalad]

This implementation allows to select the key size of the generated key ranging from 2048-4096 bits, which is using a Spinner to increment by 1024 bits. (DSA is limited to 3072 bits)

Refer to #1464

[github-actions]

Test Results

 1 755 files  ±0   1 755 suites  ±0   1h 28m 29s ⏱️ - 1m 26s
 4 170 tests ±0   4 148 ✅ ±0   22 💤 ±0  0 ❌ ±0 
13 107 runs  ±0  12 943 ✅ ±0  164 💤 ±0  0 ❌ ±0 

Results for commit 5a92d31. ± Comparison against base commit 0abe5a5.

♻️ This comment has been updated with latest results.

[HannesWell]

Thank you for this follow-up. Nice work, it works well.
I just have a few remarks below.

In general what do you think about setting the initial value to the recommended size of 4kBi for RSA and 3kBi for DSA and just allow lowering the value?
Are higher values possible for RSA too? If yes, I think we should also make that possible.

Additionally please make sure that you have formatted all new lines according to the formatter settings (unfortunately the existing code does not adhere to them). E.g. there should be a space before and after a equal-sign.

[HannesWell]

Let's keep it simple here:

Suggested change

	CVSSSH2PreferencePage_148=Key Size to Generate:
	CVSSSH2PreferencePage_148=Key size:

[HannesWell]

Better name it keySizeValue or just keySize, but then you have to rename the existing local variable with the same name to keySizeValue or alike or you just inline keySize.getSelection()

Suggested change

	private Spinner keyGenerateSize;
	private Spinner keySizeValue;

[HannesWell]

This can be simplified using KeyListener.keyPressedAdapter()

Suggested change

	keyGenerateSize.addKeyListener(new KeyAdapter() {
	@Override
	public void keyPressed(KeyEvent e) {
	e.doit = false;
	}
	});
	keySizeValue.addKeyListener(KeyListener.keyPressedAdapter(e -> e.doit = false));

[HannesWell]

Please always use braces:

Suggested change

	if (keyGenerateSize.getSelection()>DSA_KEY_SIZE)
	keyGenerateSize.setSelection(DSA_KEY_SIZE);
	if (keyGenerateSize.getSelection()>DSA_KEY_SIZE) {
	keyGenerateSize.setSelection(DSA_KEY_SIZE);
	}

[axmanalad]

In general what do you think about setting the initial value to the recommended size of 4kBi for RSA and 3kBi for DSA and just allow lowering the value?

I think this is a good idea as it initially sets it to the more secured key size than 2048 bits for developers to acknowledge. I changed the initial value to 4096 bits.

Additionally please make sure that you have formatted all new lines according to the formatter settings (unfortunately the existing code does not adhere to them). E.g. there should be a space before and after a equal-sign.

I have fixed the formatting. Thank you for clarification.

Are higher values possible for RSA too? If yes, I think we should also make that possible.

Higher values for RSA are possible. The current RSA algorithm does not seem to have a limit for the max key size it can generate. However, the main drawbacks with generating larger RSA key lengths include CPU overhead and performance issues. As you generate a larger key length, CPU runtime increases dramatically. A high-end computer could easily generate larger keys, but I would not recommend it for low-end computers.

Because of the overhead and performance, it is best to recommend using an ECC encryption for keys larger than 4096 bits since it provides an equivalent level of encryption strength as RSA with smaller key sizes and faster performance. For example, an ECC key size of 512 bits is equivalent to an RSA key size of 15360 bits. I am not sure how implementing ECC would work but it is only a thought I think would improve performance in generating keys.

I changed the max RSA key size you can generate to 15360 bits as it is equivalent to 256 security bits (really strong in security encryption); generally, higher than 15360 bits is not recommended for the sake of runtime.