the pointer to the message digest is const

doc/crypto/RSA_sign.pod

diff --git a/doc/crypto/RSA_sign.pod b/doc/crypto/RSA_sign.pod
index 71688a6..8553be8 100644
--- a/doc/crypto/RSA_sign.pod
+++ b/doc/crypto/RSA_sign.pod
@@ -8,10 +8,10 @@
 
  #include <openssl/rsa.h>
 
- int RSA_sign(int type, unsigned char *m, unsigned int m_len,
+ int RSA_sign(int type, const unsigned char *m, unsigned int m_len,
     unsigned char *sigret, unsigned int *siglen, RSA *rsa);
 
- int RSA_verify(int type, unsigned char *m, unsigned int m_len,
+ int RSA_verify(int type, const unsigned char *m, unsigned int m_len,
     unsigned char *sigbuf, unsigned int siglen, RSA *rsa);
 
 =head1 DESCRIPTION