Readd EVP_CIPHER_CTX_set_key_length.

This only applies to RC4, but it is still used by some Android code.

Change-Id: I4cf86269ffb7a230576da1bb2bfef7e1d4f234d6
Reviewed-on: https://boringssl-review.googlesource.com/1621
Reviewed-by: Adam Langley <agl@google.com>

crypto/cipher/cipher.c

@@ -573,6 +573,21 @@ int EVP_CIPHER_CTX_set_padding(EVP_CIPHER_CTX *ctx, int pad) {
   return 1;
 }
 
+int EVP_CIPHER_CTX_set_key_length(EVP_CIPHER_CTX *c, unsigned key_len) {
+  if (c->key_len == key_len) {
+    return 1;
+  }
+
+  if (key_len == 0 || !(c->cipher->flags & EVP_CIPH_VARIABLE_LENGTH)) {
+    OPENSSL_PUT_ERROR(CIPHER, EVP_CIPHER_CTX_set_key_length,
+                      CIPHER_R_INVALID_KEY_LENGTH);
+    return 0;
+  }
+
+  c->key_len = key_len;
+  return 1;
+}
+
 int EVP_CIPHER_nid(const EVP_CIPHER *cipher) { return cipher->nid; }
 
 const char *EVP_CIPHER_name(const EVP_CIPHER *cipher) {

crypto/cipher/cipher_error.c

@@ -22,6 +22,7 @@ const ERR_STRING_DATA CIPHER_error_string_data[] = {
   {ERR_PACK(ERR_LIB_CIPHER, CIPHER_F_EVP_AEAD_CTX_seal, 0), "EVP_AEAD_CTX_seal"},
   {ERR_PACK(ERR_LIB_CIPHER, CIPHER_F_EVP_CIPHER_CTX_copy, 0), "EVP_CIPHER_CTX_copy"},
   {ERR_PACK(ERR_LIB_CIPHER, CIPHER_F_EVP_CIPHER_CTX_ctrl, 0), "EVP_CIPHER_CTX_ctrl"},
+  {ERR_PACK(ERR_LIB_CIPHER, CIPHER_F_EVP_CIPHER_CTX_set_key_length, 0), "EVP_CIPHER_CTX_set_key_length"},
   {ERR_PACK(ERR_LIB_CIPHER, CIPHER_F_EVP_CipherInit_ex, 0), "EVP_CipherInit_ex"},
   {ERR_PACK(ERR_LIB_CIPHER, CIPHER_F_EVP_DecryptFinal_ex, 0), "EVP_DecryptFinal_ex"},
   {ERR_PACK(ERR_LIB_CIPHER, CIPHER_F_EVP_EncryptFinal_ex, 0), "EVP_EncryptFinal_ex"},
@@ -50,6 +51,7 @@ const ERR_STRING_DATA CIPHER_error_string_data[] = {
   {ERR_PACK(ERR_LIB_CIPHER, 0, CIPHER_R_INPUT_NOT_INITIALIZED), "INPUT_NOT_INITIALIZED"},
   {ERR_PACK(ERR_LIB_CIPHER, 0, CIPHER_R_INVALID_AD), "INVALID_AD"},
   {ERR_PACK(ERR_LIB_CIPHER, 0, CIPHER_R_INVALID_AD_SIZE), "INVALID_AD_SIZE"},
+  {ERR_PACK(ERR_LIB_CIPHER, 0, CIPHER_R_INVALID_KEY_LENGTH), "INVALID_KEY_LENGTH"},
   {ERR_PACK(ERR_LIB_CIPHER, 0, CIPHER_R_IV_TOO_LARGE), "IV_TOO_LARGE"},
   {ERR_PACK(ERR_LIB_CIPHER, 0, CIPHER_R_NO_CIPHER_SET), "NO_CIPHER_SET"},
   {ERR_PACK(ERR_LIB_CIPHER, 0, CIPHER_R_OUTPUT_ALIASES_INPUT), "OUTPUT_ALIASES_INPUT"},

include/openssl/cipher.h

@@ -261,6 +261,11 @@ OPENSSL_EXPORT int EVP_CIPHER_CTX_ctrl(EVP_CIPHER_CTX *ctx, int command,
  * to disable. */
 OPENSSL_EXPORT int EVP_CIPHER_CTX_set_padding(EVP_CIPHER_CTX *ctx, int pad);
 
+/* EVP_CIPHER_CTX_set_key_length sets the key length for |ctx|. This is only
+ * valid for ciphers that can take a variable length key. It returns one on
+ * success and zero on error. */
+OPENSSL_EXPORT int EVP_CIPHER_CTX_set_key_length(EVP_CIPHER_CTX *ctx, unsigned key_len);
+
 
 /* Cipher accessors. */
 
@@ -467,6 +472,7 @@ typedef struct evp_cipher_info_st {
 #define CIPHER_F_aead_aes_key_wrap_seal 119
 #define CIPHER_F_aead_aes_key_wrap_init 120
 #define CIPHER_F_aead_aes_key_wrap_open 121
+#define CIPHER_F_EVP_CIPHER_CTX_set_key_length 122
 #define CIPHER_R_WRAP_MODE_NOT_ALLOWED 100
 #define CIPHER_R_AES_KEY_SETUP_FAILED 101
 #define CIPHER_R_INPUT_NOT_INITIALIZED 102
@@ -490,5 +496,6 @@ typedef struct evp_cipher_info_st {
 #define CIPHER_R_UNSUPPORTED_INPUT_SIZE 120
 #define CIPHER_R_UNSUPPORTED_AD_SIZE 121
 #define CIPHER_R_UNSUPPORTED_NONCE_SIZE 122
+#define CIPHER_R_INVALID_KEY_LENGTH 123
 
 #endif  /* OPENSSL_HEADER_CIPHER_H */