What's different between RSASSA and RSAPSS padding mode?

Eddie Chang eddie.via at msa.hinet.net
Wed May 12 00:45:36 UTC 2021

  I'm new comer to openssl. Recently, I study SPDM document https://www.dmtf.org/sites/default/files/standards/documents/DSP0274_0.99a.pdf and feel confused about ReqBaseAsymAlg structure in page 49.
In this spec, I saw it can support RSASSA_4096 and RSAPSS_4096. But I check opensl source code,  rsa_padding_mode option only support pss padding. Don't have any idea about RSASSA.
Anyonce can please help to comemnt what different between RSASSA and RSAPSS is?

For testting, I can specify PSS padding with SHA256 digest for sign and verfiifcation as below command.

openssl dgst -sha512 -binary  -out sha512_out.bin  test.bin
openssl pkeyutl -sign -in sha512_out.bin -inkey gv100_rsa_3072_pvt_dbg.pem -out sig1.bin -pkeyopt digest:sha512 -pkeyopt rsa_padding_mode:pss -pkeyopt rsa_pss_saltlen:-1
openssl pkeyutl -verify -in sha512_out.bin -sigfile sig1.bin  -pkeyopt digest:sha512  -pkeyopt rsa_padding_mode:pss -pkeyopt rsa_pss_saltlen:-1 -pubin -inkey gv100_rsa_3072_pub_dbg.pem

But don't know how to test RSASSA.


Byte 0 Bit 5. TPM_ALG_RSASSA_4096
Byte 0 Bit 6. TPM_ALG_RSAPSS_4096
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