secretflow/yacl

yacl/crypto/tpre/kdf的问题

maths644311798 opened this issue · 2 comments

maths644311798 commented

在yacl/crypto/tpre/kdf.cc中，kdf的实现和SM2的文档(就是kdf.h给的文档 )不一致。这段代码

    if (i == index - 1) {
      if (key_len % 32 != 0) {
        dgst_len = (key_len) % 32;
      } else {
        dgst_len = 0;
      }
    }

中key_len被32整除时，按照文档的做法，应该是设置dgst_len = 32. 下面抄录文档这一句

若klen/v是整数，令Ha!klen/v = Haklen/v

Jamie-Cui commented

This code was contributed by external developers, it will take some time for us to verify. @xfap Would you like to take a look?

xfap commented

@maths644311798 Hi, the kdf function here is not a wrong implementation but a different impl. way. The reason for setting to 0 instead of 32, is bacause the index is setted as int index = (key_len + 32) / 32;. When key_len%32==0, there will be a redundant hash round, so the last dgst_len should set to 0.

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