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tpm12: Add a note to RSA related to EVP conversion for constant-time

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Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
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Stefan Berger 2020-10-22 15:47:39 -04:00 committed by Stefan Berger
parent 74a8ffd2f0
commit 80152a229a
1 changed files with 9 additions and 0 deletions
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src/tpm12/tpm_crypto.c
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@ -1069,6 +1069,15 @@ TPM_RESULT TPM_RSAPublicEncryptRaw(unsigned char *encrypt_data, /* output */
'signature_length' bytes are moved to 'signature'. 'signature_length' is at most
'signature_size'. signature must point to RSA_size(rsa) bytes of memory.
*/
/* Note regarding conversion to EVP_PKEY_sign for the purpose of constant-timeness:
- TPM_SS_RSASSAPKCS1v15_SHA1:
EVP_PKEY_sign() will call pkey_rsa_sign() which in turn will call RSA_sign() for
RSA_PKCS1_PADDING. This is the same as we do here.
- TPM_SS_RSASSAPKCS1v15_DER:
EVP_PKEY_sign() must not have a message digest since none of the padding choices calls
RSA_padding_add_PKCS1_type_1(), so we would have to do the padding again ourselves.
*/
TPM_RESULT TPM_RSASign(unsigned char *signature, /* output */
unsigned int *signature_length, /* output, size of signature */