Using RSAES OAEP with a custom padding parameter

[Charles T-2]

I'm attempting to write a wrapper aroung the API defined for the
trusted platform module. The Design Principles specification from the
trusted computing group (http://www.trustedcomputinggroup.org/
resources/tpm_main_specification) states that when using the
TPM_ES_RSAESOAEP_SHA1_MGF1 encryption type, that " The OAEP encoding P
parameter MUST be the 4 character string “TCPA”  ".

I use the following code when performing RSAES_OAEP encryption. How
can I modify it to set the padding parameter to "TCPA"?

std::vector<BYTE> EncryptDataUsingRSAES_OAEP_SHA( std::vector<BYTE>
vDataToEncrypt,
                                                std::vector<BYTE> vTpmRsaPubKeyModulus)
{

        std::vector<BYTE> cipher;

        CryptoPP::AutoSeededRandomPool rng;
        CryptoPP::Integer modulus(&vTpmRsaPubKeyModulus[0],
vTpmRsaPubKeyModulus.size());
        CryptoPP::RSA::PublicKey publicKey;

        publicKey.SetPublicExponent(65537); // TPM uses 65537 as public
exponent
        publicKey.SetModulus(modulus);

        CryptoPP::RSAES_OAEP_SHA_Encryptor e(publicKey);

        CryptoPP::SecByteBlock
sbbCipherText(e.CiphertextLength(vDataToEncrypt.size()));

        e.Encrypt( rng, &vDataToEncrypt[0], vDataToEncrypt.size(),
sbbCipherText.begin() );

        cipher.assign(sbbCipherText.BytePtr(), sbbCipherText.BytePtr() +
sbbCipherText.size());

        return cipher;

}

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[Jeffrey Walton-3]

On Oct 22, 6:37 am, Charles T <charles...@...> wrote:
> I'm attempting to write a wrapper aroung the API defined for the
> trusted platform module. The Design Principles specification from the
> trusted computing group (http://www.trustedcomputinggroup.org/
> resources/tpm_main_specification) states that when using the
> TPM_ES_RSAESOAEP_SHA1_MGF1 encryption type, that " The OAEP encoding P
> parameter MUST be the 4 character string “TCPA”  ".
>
> I use the following code when performing RSAES_OAEP encryption. How
> can I modify it to set the padding parameter to "TCPA"?
I don't believe modifying the padding after the fact will work well
(if at all).

For this, I believe the best course of action is to provide a
TPM_ES_RSAESOAEP_SHA1_MGF1 class. Then ne TPM padding class probably
should probably look a lot like PK_EncryptionMessageEncodingMethod or
OAEP < H, M >,

See http://www.cryptopp.com/docs/ref/annotated.html,
http://www.cryptopp.com/docs/ref/class_p_k___encryption_message_encoding_method.html
and http://www.cryptopp.com/docs/ref/class_o_a_e_p.html.

jeff

Jeff

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[Jan-126]

Hi Charles,

My solution was:

CryptoPP::ConstByteArrayParameter p("TCPA");
CryptoPP::AlgorithmParameters algParams = CryptoPP::MakeParameters(CryptoPP::Name::EncodingParameters(), p, true);

CryptoPP::RSAES_OAEP_SHA_Encryptor encryptor(publicKey);
encryptor.Encrypt(rng, plain, plainSize, enc, algParams);

So far, it is working.

Regards,
Jan

On Sat, Oct 22, 2011 at 12:37, Charles T <charleshlt@...> wrote:

I'm attempting to write a wrapper aroung the API defined for the
trusted platform module. The Design Principles specification from the
trusted computing group (http://www.trustedcomputinggroup.org/
resources/tpm_main_specification) states that when using the
TPM_ES_RSAESOAEP_SHA1_MGF1 encryption type, that " The OAEP encoding P
parameter MUST be the 4 character string “TCPA”  ".

I use the following code when performing RSAES_OAEP encryption. How
can I modify it to set the padding parameter to "TCPA"?

std::vector<BYTE> EncryptDataUsingRSAES_OAEP_SHA(       std::vector<BYTE>
vDataToEncrypt,
                                               std::vector<BYTE> vTpmRsaPubKeyModulus)
{

       std::vector<BYTE> cipher;

       CryptoPP::AutoSeededRandomPool rng;
       CryptoPP::Integer modulus(&vTpmRsaPubKeyModulus[0],
vTpmRsaPubKeyModulus.size());
       CryptoPP::RSA::PublicKey publicKey;

       publicKey.SetPublicExponent(65537); // TPM uses 65537 as public
exponent
       publicKey.SetModulus(modulus);

       CryptoPP::RSAES_OAEP_SHA_Encryptor e(publicKey);

       CryptoPP::SecByteBlock
sbbCipherText(e.CiphertextLength(vDataToEncrypt.size()));

       e.Encrypt( rng, &vDataToEncrypt[0], vDataToEncrypt.size(),
sbbCipherText.begin() );

       cipher.assign(sbbCipherText.BytePtr(), sbbCipherText.BytePtr() +
sbbCipherText.size());

       return cipher;

}

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[Charles T-2]

H Jan

That's exactly what I was looking for, and it works for me too. Thank
you.

-Charles

On Oct 24, 9:55 am, Honza Smrček <honza.smr...@...> wrote:

> Hi Charles,
>
> My solution was:
>
> CryptoPP::ConstByteArrayParameter p("TCPA");
> CryptoPP::AlgorithmParameters algParams =
> CryptoPP::MakeParameters(CryptoPP::Name::EncodingParameters(), p, true);
>
> CryptoPP::RSAES_OAEP_SHA_Encryptor encryptor(publicKey);
> encryptor.Encrypt(rng, plain, plainSize, enc, algParams);
>
> So far, it is working.
>
> Regards,
> Jan
>
>
>
> On Sat, Oct 22, 2011 at 12:37, Charles T <charles...@...> wrote:
> > I'm attempting to write a wrapper aroung the API defined for the
> > trusted platform module. The Design Principles specification from the
> > trusted computing group (http://www.trustedcomputinggroup.org/
> > resources/tpm_main_specification) states that when using the
> > TPM_ES_RSAESOAEP_SHA1_MGF1 encryption type, that " The OAEP encoding P
> > parameter MUST be the 4 character string “TCPA”  ".
>
> > I use the following code when performing RSAES_OAEP encryption. How
> > can I modify it to set the padding parameter to "TCPA"?
>
> > std::vector<BYTE> EncryptDataUsingRSAES_OAEP_SHA(       std::vector<BYTE>
> > vDataToEncrypt,
> >                                                std::vector<BYTE>
> > vTpmRsaPubKeyModulus)
> > {
>
> >        std::vector<BYTE> cipher;
>
> >        CryptoPP::AutoSeededRandomPool rng;
> >        CryptoPP::Integer modulus(&vTpmRsaPubKeyModulus[0],
> > vTpmRsaPubKeyModulus.size());
> >        CryptoPP::RSA::PublicKey publicKey;
>
> >        publicKey.SetPublicExponent(65537); // TPM uses 65537 as public
> > exponent
> >        publicKey.SetModulus(modulus);
>
> >        CryptoPP::RSAES_OAEP_SHA_Encryptor e(publicKey);
>
> >        CryptoPP::SecByteBlock
> > sbbCipherText(e.CiphertextLength(vDataToEncrypt.size()));
>
> >        e.Encrypt( rng, &vDataToEncrypt[0], vDataToEncrypt.size(),
> > sbbCipherText.begin() );
>
> >        cipher.assign(sbbCipherText.BytePtr(), sbbCipherText.BytePtr() +
> > sbbCipherText.size());
>
> >        return cipher;
>
> > }
>
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> > More information about Crypto++ and this group is available at
> >http://www.cryptopp.com.- Hide quoted text -
>
> - Show quoted text -

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