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Check that disperser uses correct blob length #1290

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merged 2 commits into from
Feb 20, 2025
Merged

Check that disperser uses correct blob length #1290

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Check that disperser uses correct blob length
litt3 Feb 19, 2025
c25f523
Merge branch 'master' into check-commitment-blob-len
litt3 Feb 20, 2025
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12 changes: 12 additions & 0 deletions api/clients/v2/disperser_client.go
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Original file line number Diff line number Diff line change
Expand Up @@ -175,6 +175,18 @@ func (c *disperserClient) DisperseBlob(
return nil, [32]byte{}, fmt.Errorf("error deserializing blob commitments: %w", err)
}
blobCommitments = *deserialized

// We need to check that the disperser used the correct length. Even once checking the commitment from the
// disperser has been implemented, there is still an edge case where the disperser could truncate trailing 0s,
// yielding the wrong blob length, but not causing commitment verification to fail. It is important that the
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is there a change on the disperser side to make sure this case is handled ?

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I don't think so- this check is intended to protect against a disperser maliciously/incorrectly truncating 0s

// commitment doesn't report a blob length smaller than expected, since this could cause payload parsing to
// fail, if the length claimed in the encoded payload header is larger than the blob length in the commitment.
lengthFromCommitment := commitments.GetBlobCommitment().GetLength()
if lengthFromCommitment != uint32(symbolLength) {
return nil, [32]byte{}, fmt.Errorf(
"blob commitment length (%d) from disperser doesn't match expected length (%d): %w",
lengthFromCommitment, symbolLength, err)
}
} else {
// if prover is configured, get commitments from prover

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