mic

mic (mina-is-cute) is a modular Go proxy for controlling outbound TLS fingerprints. It lets you pick a browser fingerprint profile and the proxy will use the corresponding uTLS preset when connecting to upstream servers, making your traffic look like a specific browser to any fingerprinting system.

Two modes are supported:

• client-front — HTTP CONNECT proxy with optional MitM TLS interception. The proxy generates a local CA, issues per-host leaf certs on the fly, terminates TLS from the client, and re-dials the target with the configured uTLS fingerprint. Standard tools (curl, browsers) work after importing the CA once.
• server-front — the proxy terminates incoming TLS (with your own cert/key), then re-dials the backend with the configured fingerprint. Useful when the client cannot be configured to use a CONNECT proxy.

---

How it works

sequenceDiagram
    participant C as Client
    participant P as mic proxy
    participant T as Target

    rect rgb(30, 30, 60)
        note over C,T: client-front mode (MitM TLS)
        C->>P: HTTP CONNECT target:443
        P->>T: TCP + uTLS handshake (configured fingerprint)
        P-->>C: 200 Connection Established
        C->>P: TLS handshake (mic-issued cert for target)
        P-->>C: TLS established
        C->>P: HTTP request (decrypted by proxy)
        P->>T: request bytes (through uTLS tunnel)
        T-->>P: HTTP response (through uTLS)
        P-->>C: HTTP response (re-encrypted for client)
    end

    rect rgb(30, 60, 30)
        note over C,T: server-front mode
        C->>P: TLS handshake (proxy cert)
        P-->>C: TLS established
        P->>T: TCP + uTLS handshake (configured fingerprint)
        C->>P: HTTP request (decrypted by proxy)
        P->>T: request bytes (through uTLS tunnel)
        T-->>P: HTTP response (through uTLS)
        P-->>C: HTTP response (re-encrypted for client)
    end

Loading

In both modes the target sees a TLS handshake that matches the configured fingerprint, not the default Go TLS fingerprint.

---

Build

go build -o mic .

---

Running

client-front

mic client --listen :8080 --fingerprint chrome-120 \
           --intercept-cert ca.pem --intercept-key ca-key.pem

--intercept-cert and --intercept-key enable MitM interception. mic generates the CA files on first run and reuses them. Import the cert once, then all traffic through the proxy is transparently intercepted and re-dialled with the configured fingerprint.

Trust the CA (pick whichever applies):

# curl — pass on every call, or set CURL_CA_BUNDLE
curl --cacert ca.pem -x http://localhost:8080 https://tlsinfo.me/json

# Debian / Ubuntu / Kali
sudo cp ca.pem /usr/local/share/ca-certificates/mic-ca.crt && sudo update-ca-certificates

# macOS
sudo security add-trusted-cert -d -r trustRoot -k /Library/Keychains/System.keychain ca.pem

After trusting, standard tools work without extra flags:

curl -x http://localhost:8080 https://tlsinfo.me/json
# check the "ja4" field — it should match the fingerprint you configured

Omit --intercept-* to run as a plain CONNECT proxy (no MitM, raw tunnel only).

server-front

Generate a cert for the proxy to present to clients:

go run $(go env GOROOT)/src/crypto/tls/generate_cert.go --host="localhost,127.0.0.1"
# produces cert.pem and key.pem

mic server --listen :8080 --backend 10.0.0.1:443 \
           --cert cert.pem --key key.pem \
           --fingerprint chrome-120

--backend, --cert, and --key are required. --fingerprint is optional; without it the proxy falls back to a randomised uTLS preset.

Available fingerprint profiles

Hashes are measured by cmd/probe against tlsinfo.me and reflect what each utls preset actually emits. Re-run the probe after upgrading the utls dependency.

Profile	JA4 hash
chrome-120	t13d1516h2_8daaf6152771_02713d6af862
chrome-120-pq	same as chrome-120¹
firefox-120	t13d1715h2_5b57614c22b0_5c2c66f702b0
safari-16	t13d2014h2_a09f3c656075_14788d8d241b
edge-106	t13d1516h2_8daaf6152771_e5627efa2ab1

¹ chrome-120-pq (post-quantum) produces the same JA4 because JA4 does not distinguish the X25519MLKEM768 key share. Use it when you specifically need the PQ key exchange behaviour regardless of fingerprint visibility.

---

Testing

# unit tests
go test ./...

# integration tests — spin up in-process TLS servers, no network required
go test -tags integration -v ./proxy/... ./fingerprint/...

The integration suite includes JA4 fingerprint verification tests: for each profile, both TestClientFront_JA4 and TestServerFront_JA4 capture the raw ClientHello sent by the proxy's uTLS engine and assert the computed JA4 hash matches the expected value. This is the offline equivalent of running cmd/probe against tlsinfo.me.

CI runs both suites on every push via .github/workflows/ci.yml.