COLDCARD vulnerability what happened, and what to do
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COLDCARD firmware PR #691 patch

coldcard-firmware-pr-691-patch

https://github.com/Coldcard/firmware/pull/691.patch

Organisation
Coinkite
Evidence role
Repository patch
Published
not established
Source changes
0
Detected differences
0
Unreviewed
0
Copies held
1

Patch content for the open firmware-side full-digest proposal. Kept separately from the conversation and review-state capture.

Every check is recorded, including checks that found no text change. A detected edit is therefore bounded between two checks. The publisher's exact save time is not observable from this record. Last checked 2 Aug 2026, 00:58 UTC.

  1. Earliest copy held Current
    seen 1 Aug 2026, 06:39 UTC · Captured here text sha256 f0c8c92072bb6216186afff4 2,044 chars
    Extracted text as captured
    From 9324b130f4e30b852e1162a7390fbe75b2f37957 Mon Sep 17 00:00:00 2001
    From: Ballance <[email protected]>
    Date: Fri, 31 Jul 2026 23:32:03 -0400
    Subject: [PATCH] fix: feed full SE digest to PRNG reseed (drop 32-bit
     truncation)
    MIME-Version: 1.0
    Content-Type: text/plain; charset=UTF-8
    Content-Transfer-Encoding: 8bit
    rng_seeding() hashed the secure-element entropy with SHA256d but then
    kept only n[0:4], handing ngu.random.reseed() a single 32-bit word. That
    throttled the secure-element contribution to 2**32 and, combined with
    reseed()'s old behaviour, left most of the generator state at fixed
    constants. Pass the whole 32-byte digest instead.
    Bumps external/libngu to a512174, which reworks random.reseed() to
    absorb a full-width seed into all generator state words.
    Ref: Block engineering disclosure, "Predictable RNG fallback and 32-bit
    reseed in COLDCARD firmware".
        Thirty-two silent bytes,
        all but four were cast aside —
        now the seed stays whole.
    ---
     external/libngu | 2 +-
     shared/mk4.py   | 6 ++++--
     2 files changed, 5 insertions(+), 3 deletions(-)
    diff --git a/external/libngu b/external/libngu
    index 537519a8..a5121743 160000
    --- a/external/libngu
    +++ b/external/libngu
    @@ -1 +1 @@
    -Subproject commit 537519a829259622ea6b0334fbafd6cae852852f
    +Subproject commit a51217432308fd9ebc7c3d54b96a5af72b71b2e9
    diff --git a/shared/mk4.py b/shared/mk4.py
    index 3a3e229d..8a4b1572 100644
    --- a/shared/mk4.py
    +++ b/shared/mk4.py
    @@ -38,13 +38,15 @@ def make_psram_fs():
     def rng_seeding():
         # seed our RNG with entropy from secure elements
    -    import callgate, ngu, ustruct
    +    import callgate, ngu

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