99 lines
3.0 KiB
C
99 lines
3.0 KiB
C
#include <openssl/evp.h>
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#include <stdio.h>
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//#cgo pkg-config: libcrypto
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extern void panic1(void);
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static void panic(const char* const msg)
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{
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fprintf(stderr, "panic in C code: %s\n", msg);
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__builtin_trap();
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}
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// https://wiki.openssl.org/index.php/EVP_Authenticated_Encryption_and_Decryption#Authenticated_Encryption_using_GCM_mode
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int chacha20poly1305_seal(
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const unsigned char* const plaintext,
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const int plaintextLen,
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const unsigned char* const authData,
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const int authDataLen,
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const unsigned char* const key,
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const int keyLen,
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const unsigned char* const iv,
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const int ivLen,
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unsigned char* const ciphertext,
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const int ciphertextBufLen)
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{
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// Create scratch space "context"
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EVP_CIPHER_CTX* ctx = EVP_CIPHER_CTX_new();
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if (!ctx) {
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panic("EVP_CIPHER_CTX_new failed");
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}
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// Set cipher
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if (EVP_EncryptInit_ex(ctx, EVP_chacha20_poly1305(), NULL, NULL, NULL) != 1) {
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panic("EVP_EncryptInit_ex set cipher failed");
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}
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// Check keyLen by trying to set it (fails if keyLen != 32)
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if (EVP_CIPHER_CTX_set_key_length(ctx, keyLen) != 1) {
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panic("keyLen mismatch");
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}
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// Set IV length so we do not depend on the default
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if (EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_SET_IVLEN, ivLen, NULL) != 1) {
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panic("EVP_CTRL_AEAD_SET_IVLEN failed");
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}
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// Set key and IV
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if (EVP_EncryptInit_ex(ctx, NULL, NULL, key, iv) != 1) {
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panic("EVP_EncryptInit_ex set key & iv failed");
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}
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// Provide authentication data
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int outLen = 0;
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if (EVP_EncryptUpdate(ctx, NULL, &outLen, authData, authDataLen) != 1) {
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panic("EVP_EncryptUpdate authData failed");
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}
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if (outLen != authDataLen) {
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panic("EVP_EncryptUpdate authData: unexpected length");
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}
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// Encrypt "plaintext" into "ciphertext"
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if (plaintextLen > ciphertextBufLen) {
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panic("plaintext overflows output buffer");
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}
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if (EVP_EncryptUpdate(ctx, ciphertext, &outLen, plaintext, plaintextLen) != 1) {
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panic("EVP_EncryptUpdate ciphertext failed");
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}
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if (outLen != plaintextLen) {
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panic("EVP_EncryptUpdate ciphertext: unexpected length");
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}
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int ciphertextLen = outLen;
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// Finalise encryption
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// Normally ciphertext bytes may be written at this stage, but this does not occur in GCM mode
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if (EVP_EncryptFinal_ex(ctx, ciphertext + plaintextLen, &outLen) != 1) {
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panic("EVP_EncryptFinal_ex failed");
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}
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if (outLen != 0) {
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panic("EVP_EncryptFinal_ex: unexpected length");
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}
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// We only support 16-byte tags
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const int tagLen = 16;
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// Get MAC tag and append it to the ciphertext
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if (ciphertextLen + tagLen > ciphertextBufLen) {
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panic("tag overflows output buffer");
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}
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if (EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_GET_TAG, tagLen, ciphertext + plaintextLen) != 1) {
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panic("EVP_CTRL_AEAD_GET_TAG failed");
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}
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ciphertextLen += tagLen;
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// Free scratch space
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EVP_CIPHER_CTX_free(ctx);
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return ciphertextLen;
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}
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