While size_t-fying let's not forget to update documentation:-)

 EVP_MD_CTX *EVP_MD_CTX_create(void);

 int EVP_DigestInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);

 int EVP_DigestUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt);

 int EVP_DigestUpdate(EVP_MD_CTX *ctx, const void *d, size_t cnt);

 int EVP_DigestFinal_ex(EVP_MD_CTX *ctx, unsigned char *md,

        unsigned int *s);