RAW RSA public key

[Nischal Bansal]

Hi All,

Our generated public key is in following format.

RSA Public Key

            modulus: 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

    public exponent: 10001

But before including in assertion or writing in a file, we are encoding the public key using below command. Because we require a byte array to insert in assertion or writing in a file.

           byte[] pub = key.getEncoded();

Our metadata is submitted with RSA_RAW, but it seems our public key is converted in below PEM format

MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA3O1-gGqUYD13y_L94XzcrRgJy458cLmKdxeXv7z1nMDEWi0REDCNFX1Uc80Al_AD7bsKAkh4cUXO1EaST12hr4IOw9fmt4H2ZkGPyqPUH0Tnhw8rSYt-yU22A-tHdab97ACxhLEIIJZWSOR90Q-OjjGm1dm9lT6ljASmF2Q4C__-U1KNf9LzxjYZV_6_U9nvYKPVtTk1O_6UgpX9YyIMOyuFPXlUgNdxDAJEpZeqhh6G3pi9jOoxufHQD7R6T1jYVQ9TeLGpUbjDDty1gZrwc4HRUlzN8hq-rF_K0GLRIoeWVhSDg7sDsCoV9OPuEpDhGwQxYi2lFGzG00fciIIsRQIDAQABPT0=

Anybody can confirm, if the above (Modulus and Exponent) mentioned public key is in RAW format and we have to send the same without encoding?

or please suggest, what's the format of the RAW Public Key and how can we send it?

[Ka Yang]

Not sure what exact implementation you used for your RSA public key class. But typically getEncoded returns the SubjectPublicKeyInfo, which is the same as the string that you shown.

According to the UAF spec, RSA RAW format is simply the concatenation of the modulus and the exponent.

FYI, here is what the spec states

UAF_ALG_KEY_RSA_2048_PSS_RAW 0x102

Raw encoded RSASSA-PSS public key [RFC3447].

The default parameters according to [RFC4055] MUST be assumed, i.e.

• Mask Generation Algorithm MGF1 with SHA256
• Salt Length of 32 bytes, i.e. the length of a SHA256 hash value.
• Trailer Field value of 1, which represents the trailer field with hexadecimal value 0xBC.

That is, [n (256 bytes), e (N-n bytes)]. Where N is the total length of the field.

This total length should be taken from the object containing this key, e.g. the TLV encoded field.

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