feat: add trivial enc/dec for strings

[tmontaigu]

This change is 

[mayeul-zama]

Reviewed 3 of 4 files at r1, all commit messages.
Reviewable status: 3 of 4 files reviewed, 3 unresolved discussions

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tfhe/src/strings/server_key/mod.rs line 62 at r1 (raw file):

    pub fn trivial_encrypt_ascii(&self, str: &str, padding: Option<u32>) -> FheString {
        let ck = self.inner.borrow();

Should be called sk

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tfhe/src/high_level_api/strings/ascii/mod.rs line 306 at r1 (raw file):

        let str = str.as_ref();
        let (sliced, padding) = if str.len() >= size {
            (&str[..size], 0)

It would be safer to return an error in that case IMO
And let the user do the shortening themselves if they need it

[tmontaigu]

Reviewable status: 3 of 4 files reviewed, 3 unresolved discussions (waiting on @mayeul-zama)

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tfhe/src/high_level_api/strings/ascii/mod.rs line 306 at r1 (raw file):

Previously, mayeul-zama wrote…

It would be safer to return an error in that case IMO
And let the user do the shortening themselves if they need it

Not sure I agree with that, the real encrypt variant does the same thing

Also to me, it would be weird that the function adds padding but refuses to truncate

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tfhe/src/strings/server_key/mod.rs line 62 at r1 (raw file):

Previously, mayeul-zama wrote…

Should be called sk

true

[mayeul-zama]

Thanks!

Reviewable status: 2 of 4 files reviewed, 1 unresolved discussion