To whom it may concern.

When reviewing the code of the GOST plug-in for openssl to see how it works,
I found that there is no check of the UKM ssl3_get_client_key_exchange.

The draft .... requires in section 3.6

" Server MUST verify, that keyBlob.transportParameters.ukm is equal to
GOSTR3411(client_random|server_random)[0..7], before decrypting the
premaster_secret. "

It seems to me that this check was omitted since I could not find it either in ssl3_get_client_key_exchange() nor in pkey_GOST94cp_decrypt().
To my opinion, the check should be done in pkey_GOST94cp_decrypt. It may be done in the following way:
1. In function ssl3_get_client_key_exchange: Generate the shared UKM from server_random and client_random the same the client is supposed to have generated it.
2. In function ssl3_get_client_key_exchange: Submit the this UKM to the EVP_PKEY_CTX instance pkey_ctx by calling
EVP_PKEY_CTX_ctrl(pkey_ctx,-1,EVP_PKEY_OP_DECRYPT,EVP_PKEY_CTRL_SET_IV,8,share d_ukm). The UKM is to be stored in the GOST specific part of pkey_ctx.

3. In function pkey_GOST94cp_decrypt: Compare the UKM stored in the EVP_PKEY_CTX instance with the one wich was parsed from the key transport blob submitted to this function call.

Who is taking care about maintenance of the GOST plug-in?

How can I contribute to that work?


André Ziermann
Senior Solution Engineer

SECUDE IT Security GmbH
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64293 Darmstadt / Germany

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