[openssl-users] Using RSA_PKCS1_OAEP_PADDING with high level EVP_Seal functions

[Daniel Knoppel]

Thanks for the reply! Unfortunately I'm not sure I understand what
you're saying.

If EVP_Seal* is an old function, is there a new function with which we
can accomplish the same functionality?

What I mean is that the EVP_PKEY_encrypt() looks functionally the same
as RSA_public_encrypt() (just encrypting using a public key), so it
doesn't help with encrypting bulk data like the EVP_Seal*() functions.

For instance, with EVP_PKEY_encrypt users still have to deal with
symmetric key and iv generation, something that EVP_Seal*() does for you
(i.e. so you can't get it wrong).

The official documentation[1] even hints that you should be using
EVP_Seal*():
"For encryption and decryption see EVP_PKEY_encrypt and EVP_PKEY_decrypt
respectively. However, note that these functions perform encryption and
decryption only. As public key encryption is an expensive operation,
normally you would wrap an encrypted message in a "digital envelope"
using the EVP_SealInit and EVP_OpenInit functions."

Best regards,

Daniel
[1] https://www.openssl.org/docs/manmaster/crypto/evp.html

On 8-9-2016 21:18, Dr. Stephen Henson wrote:
> On Wed, Sep 07, 2016, Daniel Knoppel wrote:
> 
>> Dear all,
>>
>> I was wondering about two things:
>>
>> 1. Can the EVP_Seal*() functions be told to use RSA_PKCS1_OAEP_PADDING,
>> or do I need to stick with the lower level RSA_public_encrypt()?
>>
>> >From the source code it seems to me that RSA_PKCS1_PADDING is hardcoded
>> because EVP_SealInit() [1] calls EVP_PKEY_encrypt_old() [2], which in
>> turn has the line with hardcoded padding:
>>
>> ret = RSA_public_encrypt(key_len, key, ek, EVP_PKEY_get0_RSA(pubk),
>> RSA_PKCS1_PADDING);
>>
> 
> EVP_Seal*() is an old function hard coded to use RSA_PKCS1_PADDING as you've
> observed.
> 
> You don't need to use the low level RSA_public_encrypt() function for
> OAEP. Instead use the EVP_PKEY APIs EVP_PKEY_encrypt() and EVP_PKEY_decrypt()
> with the padding mode modified and appropriate parameters set.
> 
> Steve.
> --
> Dr Stephen N. Henson. OpenSSL project core developer.
> Commercial tech support now available see: http://www.openssl.org
>