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add documentation of the new RSA API functions

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Steffen Jaeckel 2014-08-30 17:19:20 +02:00
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crypt.tex
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@ -3377,6 +3377,14 @@ in \textit{out} and the size of the result in \textit{outlen}. \textit{which} is
Note: the output of this function is zero--padded as per PKCS \#1 specification. This allows this routine to work with PKCS \#1 padding functions properly.
\subsection{RSA Key Size}
To fetch the key size of an RSA key, use the following function:
\index{rsa\_get\_size()}
\begin{verbatim}
int rsa_get_size(rsa_key *key);
\end{verbatim}
This can be used to determine the modulus size of an RSA key.
\mysection{RSA Key Encryption}
Normally RSA is used to encrypt short symmetric keys which are then used in block ciphers to encrypt a message.
To facilitate encrypting short keys the following functions have been provided.
@ -3541,6 +3549,22 @@ and the extracted hash is compared against the message digest pointed to by \tex
If the RSA decoded data is not a valid PSS message, or if the PSS decoded hash does not match the \textit{msghash}
value, \textit{res} is set to $0$. Otherwise, if the function succeeds, and signature is valid \textit{res} is set to $1$.
\subsection{RSA Signature Salt Length}
The v2.1 signature algorithm requires a salt length to be able to properly
encode resp. decode. To fetch the maximum possible salt length this function
is provided:
\index{rsa\_sign\_saltlen\_get\_max()}
\begin{verbatim}
int rsa_sign_saltlen_get_max(int hash_idx, rsa_key *key);
\end{verbatim}
As stated in the PKCS#1 RFC3447 "Typical salt lengths in octets are hLen
(the length of the output of the hash function Hash) and 0".
This function is provided to be able to use other lengths as well and to make
sure at runtime that the RSA key can handle the desired salt length.
\subsection{Extended Verification}
As of v1.15, the library supports both v1.5 and v2.1 signature verification. The extended signature verification function has the following prototype: