stupidgcm: replace chacha20poly1305_seal with generic aead_seal

internal/stupidgcm/Makefile

@@ -4,4 +4,4 @@ gcc:
 
 .PHONY: format
 format:
-	clang-format --style=WebKit -i *.c
+	clang-format --style=WebKit -i *.c *.h

internal/stupidgcm/chacha.c

@@ -1,9 +1,8 @@
+#include "chacha.h"
 #include <openssl/evp.h>
 #include <stdio.h>
 //#cgo pkg-config: libcrypto
 
-extern void panic1(void);
-
 static void panic(const char* const msg)
 {
     fprintf(stderr, "panic in C code: %s\n", msg);
@@ -11,7 +10,8 @@ static void panic(const char* const msg)
 }
 
 // https://wiki.openssl.org/index.php/EVP_Authenticated_Encryption_and_Decryption#Authenticated_Encryption_using_GCM_mode
-int chacha20poly1305_seal(
+int aead_seal(
+    const enum aeadType cipherId,
     const unsigned char* const plaintext,
     const int plaintextLen,
     const unsigned char* const authData,
@@ -23,6 +23,18 @@ int chacha20poly1305_seal(
     unsigned char* const ciphertext,
     const int ciphertextBufLen)
 {
+    const EVP_CIPHER* evpCipher = NULL;
+    switch (cipherId) {
+    case aeadTypeChacha:
+        evpCipher = EVP_chacha20_poly1305();
+        break;
+    case aeadTypeGcm:
+        evpCipher = EVP_aes_256_gcm();
+        break;
+    default:
+        panic("unknown cipherId");
+    }
+
     // Create scratch space "context"
     EVP_CIPHER_CTX* ctx = EVP_CIPHER_CTX_new();
     if (!ctx) {
@@ -30,7 +42,7 @@ int chacha20poly1305_seal(
     }
 
     // Set cipher
-    if (EVP_EncryptInit_ex(ctx, EVP_chacha20_poly1305(), NULL, NULL, NULL) != 1) {
+    if (EVP_EncryptInit_ex(ctx, evpCipher, NULL, NULL, NULL) != 1) {
         panic("EVP_EncryptInit_ex set cipher failed");
     }
 

internal/stupidgcm/chacha.h

@@ -0,0 +1,17 @@
+enum aeadType {
+    aeadTypeChacha = 1,
+    aeadTypeGcm = 2,
+};
+
+int aead_seal(
+    const enum aeadType cipherId,
+    const unsigned char* const plaintext,
+    const int plaintextLen,
+    const unsigned char* const authData,
+    const int authDataLen,
+    const unsigned char* const key,
+    const int keyLen,
+    const unsigned char* const iv,
+    const int ivLen,
+    unsigned char* const ciphertext,
+    const int ciphertextBufLen);

internal/stupidgcm/stupidchacha.go

@@ -13,12 +13,8 @@ import (
 
 /*
 #include <openssl/evp.h>
+#include "chacha.h"
 #cgo pkg-config: libcrypto
-int chacha20poly1305_seal(const unsigned char * const plaintext, const int plaintextLen,
-                const unsigned char * const authData, const int authDataLen,
-                const unsigned char * const key, const int keyLen,
-                const unsigned char * const iv, const int ivLen,
-                unsigned char * const ciphertext, const int ciphertextBufLen);
 */
 import "C"
 
@@ -75,7 +71,8 @@ func (g *stupidChacha20poly1305) Seal(dst, iv, in, authData []byte) []byte {
 		buf = make([]byte, outLen)
 	}
 
-	C.chacha20poly1305_seal((*C.uchar)(&in[0]),
+	C.aead_seal(C.aeadTypeChacha,
+		(*C.uchar)(&in[0]),
 		C.int(len(in)),
 		(*C.uchar)(&authData[0]),
 		C.int(len(authData)),