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-rw-r--r--internal/stupidgcm/chacha.c98
1 files changed, 98 insertions, 0 deletions
diff --git a/internal/stupidgcm/chacha.c b/internal/stupidgcm/chacha.c
new file mode 100644
index 0000000..c85cf78
--- /dev/null
+++ b/internal/stupidgcm/chacha.c
@@ -0,0 +1,98 @@
+#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);
+ __builtin_trap();
+}
+
+// https://wiki.openssl.org/index.php/EVP_Authenticated_Encryption_and_Decryption#Authenticated_Encryption_using_GCM_mode
+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)
+{
+ // Create scratch space "context"
+ EVP_CIPHER_CTX* ctx = EVP_CIPHER_CTX_new();
+ if (!ctx) {
+ panic("EVP_CIPHER_CTX_new failed");
+ }
+
+ // Set cipher
+ if (EVP_EncryptInit_ex(ctx, EVP_chacha20_poly1305(), NULL, NULL, NULL) != 1) {
+ panic("EVP_EncryptInit_ex set cipher failed");
+ }
+
+ // Check keyLen by trying to set it (fails if keyLen != 32)
+ if (EVP_CIPHER_CTX_set_key_length(ctx, keyLen) != 1) {
+ panic("keyLen mismatch");
+ }
+
+ // Set IV length so we do not depend on the default
+ if (EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_SET_IVLEN, ivLen, NULL) != 1) {
+ panic("EVP_CTRL_AEAD_SET_IVLEN failed");
+ }
+
+ // Set key and IV
+ if (EVP_EncryptInit_ex(ctx, NULL, NULL, key, iv) != 1) {
+ panic("EVP_EncryptInit_ex set key & iv failed");
+ }
+
+ // Provide authentication data
+ int outLen = 0;
+ if (EVP_EncryptUpdate(ctx, NULL, &outLen, authData, authDataLen) != 1) {
+ panic("EVP_EncryptUpdate authData failed");
+ }
+ if (outLen != authDataLen) {
+ panic("EVP_EncryptUpdate authData: unexpected length");
+ }
+
+ // Encrypt "plaintext" into "ciphertext"
+ if (plaintextLen > ciphertextBufLen) {
+ panic("plaintext overflows output buffer");
+ }
+ if (EVP_EncryptUpdate(ctx, ciphertext, &outLen, plaintext, plaintextLen) != 1) {
+ panic("EVP_EncryptUpdate ciphertext failed");
+ }
+ if (outLen != plaintextLen) {
+ panic("EVP_EncryptUpdate ciphertext: unexpected length");
+ }
+ int ciphertextLen = outLen;
+
+ // Finalise encryption
+ // Normally ciphertext bytes may be written at this stage, but this does not occur in GCM mode
+ if (EVP_EncryptFinal_ex(ctx, ciphertext + plaintextLen, &outLen) != 1) {
+ panic("EVP_EncryptFinal_ex failed");
+ }
+ if (outLen != 0) {
+ panic("EVP_EncryptFinal_ex: unexpected length");
+ }
+
+ // We only support 16-byte tags
+ const int tagLen = 16;
+
+ // Get MAC tag and append it to the ciphertext
+ if (ciphertextLen + tagLen > ciphertextBufLen) {
+ panic("tag overflows output buffer");
+ }
+ if (EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_GET_TAG, tagLen, ciphertext + plaintextLen) != 1) {
+ panic("EVP_CTRL_AEAD_GET_TAG failed");
+ }
+ ciphertextLen += tagLen;
+
+ // Free scratch space
+ EVP_CIPHER_CTX_free(ctx);
+
+ return ciphertextLen;
+}