BN_CTX bindings
diff --git a/cryptography/hazmat/bindings/openssl/bignum.py b/cryptography/hazmat/bindings/openssl/bignum.py
index a40397d..48350a3 100644
--- a/cryptography/hazmat/bindings/openssl/bignum.py
+++ b/cryptography/hazmat/bindings/openssl/bignum.py
@@ -44,6 +44,13 @@
BIGNUM *BN_new(void);
void BN_free(BIGNUM *);
+BN_CTX *BN_CTX_new(void);
+void BN_CTX_free(BN_CTX *);
+
+void BN_CTX_start(BN_CTX *);
+BIGNUM *BN_CTX_get(BN_CTX *);
+void BN_CTX_end(BN_CTX *);
+
BIGNUM *BN_copy(BIGNUM *, const BIGNUM *);
BIGNUM *BN_dup(const BIGNUM *);