diff --git a/src/crypto.c b/src/crypto.c
index a404aa7c..07e82b80 100644
--- a/src/crypto.c
+++ b/src/crypto.c
@@ -34,6 +34,25 @@
 #include "sha1.h"
 #include "crypto.h"
 
+/* 802.11, Section 11.6.2, Table 11-4 */
+int crypto_cipher_key_len(enum crypto_cipher cipher)
+{
+	switch (cipher) {
+	case CRYPTO_CIPHER_WEP40:
+		return 5;
+	case CRYPTO_CIPHER_WEP104:
+		return 13;
+	case CRYPTO_CIPHER_TKIP:
+		return 32;
+	case CRYPTO_CIPHER_CCMP:
+		return 16;
+	case CRYPTO_CIPHER_BIP:
+		return 16;
+	};
+
+	return 0;
+}
+
 int crypto_psk_from_passphrase(const char *passphrase,
 				const unsigned char *ssid, size_t ssid_len,
 				unsigned char *out_psk)
diff --git a/src/crypto.h b/src/crypto.h
index a78ff942..e0b2df35 100644
--- a/src/crypto.h
+++ b/src/crypto.h
@@ -23,6 +23,16 @@
 #include <stddef.h>
 #include <stdbool.h>
 
+enum crypto_cipher {
+	CRYPTO_CIPHER_WEP40,
+	CRYPTO_CIPHER_WEP104,
+	CRYPTO_CIPHER_TKIP,
+	CRYPTO_CIPHER_CCMP,
+	CRYPTO_CIPHER_BIP,
+};
+
+int crypto_cipher_key_len(enum crypto_cipher cipher);
+
 int crypto_psk_from_passphrase(const char *passphrase,
 				const unsigned char *ssid, size_t ssid_len,
 				unsigned char *out_psk);