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GeezerVison is showing github.com — Implement Type-1 decryption by jkseppan · Pull Request #20634 · matplotlib/matplotlib

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@jkseppan

@jkseppan jkseppan commented Jul 12, 2021 •
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PR Summary

Implement decryption of the encrypted part of Type-1 fonts. This is a prerequisite of subsetting (#127) although that will need a lot more code.

I looked at using fonttools for Type-1 subsetting, but it seems to lack much of the functionality needed for that, although it does implement this decryption algorithm. (The code in this PR is completely my own implementation.)

cc @aitikgupta - subsetting TTF fonts is more important than Type-1 since it affects a lot more users, but if you want to take a look at Type-1 subsetting, this is the first step

PR Checklist

  • Has pytest style unit tests (and pytest passes).
  • Is Flake 8 compliant (run flake8 on changed files to check).
  • New features are documented, with examples if plot related.
  • Documentation is sphinx and numpydoc compliant (the docs should build without error).
  • Conforms to Matplotlib style conventions (install flake8-docstrings and run flake8 --docstring-convention=all).
  • New features have an entry in doc/users/next_whats_new/ (follow instructions in README.rst there).
  • API changes documented in doc/api/next_api_changes/ (follow instructions in README.rst there).

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@jkseppan
jkseppan force-pushed the type1-decrypt branch from dec2657 to 604c8a4 Compare July 12, 2021 18:16
@jkseppan jkseppan added the topic: text/fonts label Jul 12, 2021
@jkseppan
jkseppan force-pushed the type1-decrypt branch from 604c8a4 to 41bb30c Compare July 12, 2021 19:26
jklymak
jklymak approved these changes Jul 21, 2021
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Seems fine to me beyond the small minor points.

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Comment thread doc/users/next_whats_new/type1decrypt.rst Outdated
@@ -0,0 +1,8 @@
Type1Font objects now decrypt the encrypted part

@jklymak jklymak Jul 21, 2021

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I wonder if this should be an API note rather than whats-new. I'm not sure this is really a user-facing feature, even if it is public.

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Comment thread lib/matplotlib/type1font.py
@staticmethod
def _decrypt(ciphertext, key, ndiscard=4):
"""
Decrypt ciphertext using the Type-1 font algorithm

@jklymak jklymak Jul 21, 2021

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Is there a reference to the "encryption" we can add here? Also is decrypt the right word? Its really just obfuscated at this point?

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@jkseppan jkseppan Jul 22, 2021

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The reference is the manual referenced in the file docstring. The manual uses the words "encrypt" and "decrypt", so I think it is best to follow its terminology.

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@jkseppan
jkseppan force-pushed the type1-decrypt branch from 41bb30c to b81313f Compare July 22, 2021 10:12
@jkseppan jkseppan mentioned this pull request Jul 22, 2021
Improve Type-1 font parsing #20715
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@jkseppan
jkseppan force-pushed the type1-decrypt branch from a1826bb to b9e71c5 Compare July 22, 2021 12:23
@anntzer

anntzer commented Jul 22, 2021

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Could we consider defering most of type1's handling to fonttools as well instead?
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@jkseppan

jkseppan commented Jul 22, 2021

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Could we consider defering most of type1's handling to fonttools as well instead?

I tried - its type-1 implementation is very incomplete and not sufficient for subsetting.
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@anntzer

anntzer commented Jul 22, 2021

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OK then.
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anntzer
anntzer reviewed Jul 22, 2021
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Comment thread lib/matplotlib/type1font.py Resolved

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anntzer
anntzer reviewed Jul 22, 2021
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Comment thread lib/matplotlib/type1font.py Resolved

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anntzer
anntzer approved these changes Jul 22, 2021
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Just some minor points, please address them (or explicitly reject them if you don't want to make the changes), then this can be self-merged.

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jkseppan added a commit to jkseppan/matplotlib that referenced this pull request Jul 22, 2021
@jkseppan
Type-1 subsetting
b66579d 
With this I can produce smaller pdf files with usetex in some small
tests, but this obviously needs more extensive testing, thus marking
as draft.

On top of matplotlib#20634 and matplotlib#20715. Closes matplotlib#127.
@jkseppan jkseppan mentioned this pull request Jul 22, 2021
Type-1 font subsetting #20716
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@jkseppan
jkseppan force-pushed the type1-decrypt branch from b9e71c5 to 06845a4 Compare July 22, 2021 13:55
@jkseppan

jkseppan commented Jul 22, 2021

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Thanks for the review @anntzer - I made the changes. I'll wait for the CI to complete before merging.
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@jklymak

jklymak commented Jul 22, 2021

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@jkseppan if one of us doesn't get to it, feel free to self-merge when CI is all green.
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anntzer
anntzer reviewed Jul 22, 2021
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Comment thread lib/matplotlib/type1font.py Resolved

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jkseppan added 2 commits July 22, 2021 17:24
@jkseppan
Implement Type-1 decryption
3863a75 
This is a prerequisite of subsetting.
@jkseppan
Fix two crashes on slightly broken font files
e095ccd 
The zeros at the end are not needed by our implementation so don't
crash if there are too few.

Always pass an even number of bytes to unhexlify.
@jkseppan
jkseppan force-pushed the type1-decrypt branch from 06845a4 to e095ccd Compare July 22, 2021 14:24
jkseppan added a commit to jkseppan/matplotlib that referenced this pull request Jul 22, 2021
@jkseppan
Type-1 subsetting
6546417 
With this I can produce smaller pdf files with usetex in some small
tests, but this obviously needs more extensive testing, thus marking
as draft.

On top of matplotlib#20634 and matplotlib#20715. Closes matplotlib#127.
@jkseppan
jkseppan merged commit 57db5a7 into matplotlib:master Jul 22, 2021
@jkseppan
jkseppan deleted the type1-decrypt branch July 22, 2021 15:56
@QuLogic QuLogic added this to the v3.5.0 milestone Aug 12, 2021
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@anntzer anntzer anntzer approved these changes
@jklymak jklymak jklymak approved these changes

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@jkseppan @anntzer @jklymak @QuLogic
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