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when the below function is used to generate RSA key pair of 1024 bits.

rsa_key = RSA_generate_key ( 1024, 3, NULL, NULL );

keyPair = BIO_new ( BIO_s_mem ( ) );

PEM_write_bio_RSAPrivateKey(keyPair, rsa_key, NULL, NULL, 0, NULL, NULL);

keyPair_len = BIO_pending(keyPair);


Then keyPair_len obtained is not 1024, it is 882. what is the reason that it got reduced.

By using RSA_generate_key() function are we generating key pair or only private key. If so when we extract private and public keys from that it is generating private and public keys of different lengths.

evp_key = EVP_PKEY_new();
ret = EVP_PKEY_assign_RSA ( evp_key, rsa_key );
pri = BIO_new ( BIO_s_mem ( ) );
pub = BIO_new ( BIO_s_mem ( ) );

PEM_write_bio_PrivateKey ( pri, evp_key, NULL, NULL, 0, NULL, NULL );
PEM_write_bio_PUBKEY ( pub, evp_key );

pri_len = BIO_pending(pri);
pub_len = BIO_pending(pub);


The lengths of pri_len pub_len are 916 and 272 respectively. Can anyone help in understanding the reason why this is so?
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