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src: hide kMaxDigestMultiplier outside HKDF impl #46206

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merged 1 commit into from Jan 16, 2023
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src: hide kMaxDigestMultiplier outside HKDF impl #46206

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4 changes: 4 additions & 0 deletions src/crypto/crypto_hkdf.cc
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Expand Up @@ -87,6 +87,10 @@ Maybe<bool> HKDFTraits::AdditionalConfig(
: info.ToByteSource();

params->length = args[offset + 4].As<Uint32>()->Value();
// HKDF-Expand computes up to 255 HMAC blocks, each having as many bits as the
// output of the hash function. 255 is a hard limit because HKDF appends an
// 8-bit counter to each HMAC'd message, starting at 1.
constexpr size_t kMaxDigestMultiplier = 255;
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Nit: It might be better suited to make this a static, but just as suggestion.

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@tniessen tniessen Jan 15, 2023 •
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It was static before and I intentionally removed the keyword. Could you elaborate on why static would be beneficial here?

My understanding is that since kMaxDigestMultiplier is not ODR-used, not making it static allows the compiler to completely eliminate any storage space for it, but I might be wrong about this.

size_t max_length = EVP_MD_size(params->digest) * kMaxDigestMultiplier;
if (params->length > max_length) {
THROW_ERR_CRYPTO_INVALID_KEYLEN(env);
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2 changes: 0 additions & 2 deletions src/crypto/crypto_hkdf.h
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Expand Up @@ -11,8 +11,6 @@

namespace node {
namespace crypto {
static constexpr size_t kMaxDigestMultiplier = 255;

struct HKDFConfig final : public MemoryRetainer {
CryptoJobMode mode;
size_t length;
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