The tpm plugin offers random number generation

The tpm plugin can be used to derive true random numbers from a
TPM 2.0 device. The get_random method must be explicitly enabled
in strongswan.conf with the plugin.tpm.use_rng = yes option.

src/libtpmtss/tpm_tss.h

@@ -134,6 +134,15 @@ struct tpm_tss_t {
 				 signature_scheme_t scheme, chunk_t data, chunk_t pin,
 				 chunk_t *signature);
 
+	/**
+	 * Get random bytes from the TPM
+	 *
+	 * @param bytes			number of random bytes requested
+	 * @param buffer		buffer where the random bytes are written into
+	 * @return				TRUE if random bytes could be delivered
+	 */
+	bool (*get_random)(tpm_tss_t *this, size_t bytes, uint8_t *buffer);
+
 	/**
 	 * Destroy a tpm_tss_t.
 	 */