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lukevalenta
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Is this worth updating to make this constant-time like crypto/internal/nistec is?
| // - A new method included for double-point multiplication. | ||
| // | ||
| // Note: the scalar-multiplication routines in this package are not fully | ||
| // constant time. |
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Just to add a little more detail:
Suggested change
| // constant time. | |
| // constant time. Execution time and memory access can depend on the value of | |
| // the secret scalar, so avoid using these routines with secret scalars where | |
| // timing side-channels are a concern. |
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Claude suggested this as a description of where the non-constant timedness comes from. I have not carefully checked though, so if it doesn't sound right please ignore:
// Note: the scalar-multiplication routines in this package are not fully
// constant time. The windowed point arithmetic itself is constant time, but
// the scalar reduction and recoding (reduceScalar and toOdd) use variable-time
// math/big operations, so execution time and memory allocations can depend on
// the value of the secret scalar. Avoid using these routines with secret
// scalars where timing side-channels are a concern.
| } | ||
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| // ScalarMult returns (Qx,Qy)=k*(Px,Py) where k is a number in big-endian form. | ||
| // It is not fully constant time. |
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| // It is not fully constant time. | |
| // It is not fully constant time; see the package documentation for details. |
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| // ScalarBaseMult returns k*G, where G is the base point of the group | ||
| // and k is an integer in big-endian form. | ||
| // and k is an integer in big-endian form. It is not fully constant time. |
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| // and k is an integer in big-endian form. It is not fully constant time. | |
| // and k is an integer in big-endian form. It is not fully constant time; | |
| // see the package documentation for details. |
lukevalenta
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Jul 15, 2026
Co-authored-by: Luke Valenta <lvalenta@cloudflare.com>
cjpatton
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Jul 22, 2026
Issue #657 asked for an explicit README-level warning that some experimental CIRCL packages are not constant time. PRs #638 and #651 added per-package constant-time caveats to eight packages, but the README's Security Disclaimer still only mentioned that the library is experimental — it never mentioned constant time. Add a "Constant-Time Caveats" subsection under the existing Security Disclaimer, pointing readers at the per-package notes in group, oprf, blindsign/blindrsa/partiallyblindrsa, secretsharing, tss/rsa, zk/dl, zk/dleq, and ecc/p384. Documentation-only change: no source files touched, no API change, no tests added. Refs: #657
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