Get generic password from MacOS Keychain with C

get_generic_password.c

// Build: gcc -framework Security -framework Foundation -o get_generic_password get_generic_password.c
// Usage: ./get_generic_password <service name>

#include <CoreFoundation/CoreFoundation.h>
#include <Security/Security.h>

OSStatus getCredentialByServiceName(const char *serviceName, CFTypeRef *credential) {
    CFStringRef cfServiceName = CFStringCreateWithCString(kCFAllocatorDefault, serviceName, kCFStringEncodingUTF8);

    const void* keys[] = { kSecClass, kSecAttrService, kSecReturnAttributes, kSecReturnData, kSecMatchLimit };
    const void* values[] = { kSecClassGenericPassword, cfServiceName, kCFBooleanTrue, kCFBooleanTrue, kSecMatchLimitOne };

    CFDictionaryRef query = CFDictionaryCreate(kCFAllocatorDefault, (const void**) keys, (const void**) values, 5, NULL, NULL);

    OSStatus result = SecItemCopyMatching(query, credential);
    CFRelease(cfServiceName);
    CFRelease(query);
    return result;
}

void getString(CFStringRef cfString, char **buffer) {
    const char *str = CFStringGetCStringPtr(cfString, kCFStringEncodingUTF8);
    if (str != NULL) {
        *buffer = malloc(strlen(str) + 1);
        strcpy(*buffer, str);
    } else {
        CFIndex length = CFStringGetLength(cfString);
        CFIndex stringLength = length * sizeof(UniChar) + 1;
        *buffer = malloc(stringLength);
        CFStringGetCString(cfString, *buffer, stringLength, kCFStringEncodingUTF8);
    }
}

int main(int argc, const char* argv[]) {
    if (argc < 2) {
        fprintf(stderr, "Usage: ./get_generic_password <service name>");
        return 1;
    }

    const char *serviceName = argv[1];

    CFTypeRef credential = NULL;
    OSStatus result = getCredentialByServiceName(serviceName, &credential);
    
    if (result == errSecSuccess) {
        CFStringRef cfAccount = (CFStringRef) CFDictionaryGetValue(credential, kSecAttrAccount);
        if (cfAccount != NULL) {
            char *account = NULL;
            getString(cfAccount, &account);
            printf("Account: %s\n", account);
            free(account);
        }

        CFDataRef cfPassword = (CFDataRef) CFDictionaryGetValue(credential, kSecValueData);
        if (cfPassword != NULL) {
            long length = CFDataGetLength(cfPassword);
            uint8_t *buffer = malloc(length);
            CFDataGetBytes(cfPassword, CFRangeMake(0, length), buffer);
            printf("Password: %.*s\n", (int)length, buffer);
            free(buffer);
            buffer = NULL;
        }

        CFRelease(credential);
    }

    return 0;
}