Zoom rolled their own encryption scheme, transmit keys through servers in China

Re:Zoom rolled their own encryption scheme, transmit keys th... by tptacek on Saturday April 04, 2020 @07:58PM (#22782521)

This is useful. Thanks! Out of ~22,000 AES blocks, this has ~1000 colliding blocks:

    04608c1c211004608c1c00000007419b: 4 samples
    1004608c1c211004608c1c0000000741: 4 samples
    0963211004608c1c211004608c1c0000: 5 samples
    33c00963211004608c1c211004608c1c: 5 samples
    63211004608c1c211004608c1c000000: 5 samples
    f7df7df7df7df7df7df7df7df7df7df7: 5 samples
    0001000003ff0000000e000004000000: 6 samples
    211004608c1c211004608c1c00000007: 7 samples
    c00963211004608c1c211004608c1c00: 8 samples
    0001000003ff00000014000004000000: 9 samples
    0001000003ff0000000d000004000000: 25 samples
    75d75d75d75d75d75d75d75d75d75d75: 31 samples
    5d75d75d75d75d75d75d75d75d75d75d: 33 samples
    00000b0000000b0000000b0000000b00: 34 samples
    d75d75d75d75d75d75d75d75d75d75d7: 34 samples
    7f3f9fcfe7f3f9fcfe7f3f9fcfe7f3f9: 39 samples
    f3f9fcfe7f3f9fcfe7f3f9fcfe7f3f9f: 40 samples
    9fcfe7f3f9fcfe7f3f9fcfe7f3f9fcfe: 42 samples
    cfe7f3f9fcfe7f3f9fcfe7f3f9fcfe7f: 42 samples
    fcfe7f3f9fcfe7f3f9fcfe7f3f9fcfe7: 42 samples
    e7f3f9fcfe7f3f9fcfe7f3f9fcfe7f3f: 43 samples
    f9fcfe7f3f9fcfe7f3f9fcfe7f3f9fcf: 43 samples
    fe7f3f9fcfe7f3f9fcfe7f3f9fcfe7f3: 46 samples
    3f9fcfe7f3f9fcfe7f3f9fcfe7f3f9fc: 47 samples
    aebaebaebaebaebaebaebaebaebaebae: 60 samples
    baebaebaebaebaebaebaebaebaebaeba: 63 samples
    00000000000000000000000000000000: 69 samples
    ebaebaebaebaebaebaebaebaebaebaeb: 73 samples
    00060000000600000006000000060000: 147 samples

The collisions occur in runs, so, for instance, there's a run of ~40 "fcfe7f3f9fcfe7f3f9fcfe7f3f9fcfe7"'s towards the end of the file.

I-frame macroblocks in H.264 are DCT'd, like a JPEG; I have no intuition for what the repeats would signify, except that the encoding is deterministic and, I guess, within an I-frame, stateless? So identical samples will show up in the output?

(It might be easy to instrument an H.264 decoder to get an indication of what frame I'm in when I see a collision, which is I guess what I'll do next).

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Re:Zoom rolled their own encryption scheme, transmit keys th... by pvg on Sunday April 05, 2020 @03:05PM (#22787664)

Did you ever find some sort of reasonable 'live streaming' type profile for encoding? I noticed ffmpeg's default seems to be putting more work into this than you'd expect from a realtime encoder which, in theory at least, might lead to fewer collisions than in a 'realistic' situation. I think tialaramex made a similar point somewhere upthread.

I don't think it would make a huge difference but the numbers might be higher/more representative. Another way might be to just capture zoom traffic of someone's Quarterly Synergies presentation or whatnot.

Edit: also thought of a silly upper-bound test for Team Penguin - you get plaintext of every colliding block in the stream. How much penguin can you get out of that?

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Re:Zoom rolled their own encryption scheme, transmit keys th... by tptacek on Saturday April 04, 2020 @10:35PM (#22783303)

I'm just noticing, by the way, that one of the repeats in this test pattern video is the same as the repeat you observed in the Star Wars opening crawl, so presumably that has nothing to do with content.

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