MD5 vs SHA-256 - khi nao dung moi ham bam
MD5 va SHA-256 tao ra dau van tay kich thuoc co dinh cua du lieu dau vao tuy y. Chung trong co ve hoan doi duoc tu ben ngoai - dan van ban, lay hex - nhung giai quyet cac van de khac nhau. MD5 la mot dau van tay nhanh, bi pha vo ma hoa, phu hop cho kiem tra tinh toan ven khong doi khang. SHA-256 la mot bam hien dai, bao mat ma hoa, dung o bat cu noi nao mot ke tan cong co the co gang gia mao mot va cham. Chon dung cho cong viec tiet kiem thoi gian CPU va ngan ngua khoang trong bao mat thuc su.
Mot ham bam thuc su lam gi
Mot ham bam lay byte dau vao co bat ky do dai nao va tra ve mot digest do dai co dinh. Cung dau vao luon tao ra cung digest. Thay doi mot bit duy nhat cua dau vao tao ra mot digest hoan toan khac (hieu ung tuyet le). Digest la mot chieu - ban khong the tai tao dau vao tu digest.
MD5 tra ve 128 bit (32 ky tu hex). SHA-256 tra ve 256 bit (64 ky tu hex). Ca hai deu xac dinh. Ca hai deu nhanh. Ca hai khong tiet lo gi ve cau truc dau vao tu dau ra.
So sanh canh nhau
| Thuoc tinh | MD5 | SHA-256 |
|---|---|---|
| Do dai digest | 128 bit (32 ky tu hex) | 256 bit (64 ky tu hex) |
| Thiet ke | 1991 (Ron Rivest) | 2001 (NSA, FIPS 180-2) |
| Gia dinh | dong MD4 | gia dinh SHA-2 |
| Khang va cham | Bi pha tu 2004 (Wang et al.); va cham thuc te trong vai giay | Khong biet va cham thuc te; ~2128 phep tinh de tim mot |
| Khang preimage thu hai | Yeu di nhung khong co tan cong thuc te cho dau vao da tinh truoc | Manh; ~2256 phep tinh |
| Toc do (x86-64 hien dai) | ~500 MB/s moi loi | ~300 MB/s moi loi (SHA-NI: ~1,5 GB/s) |
| Tang toc phan cung | Khong co lenh chuyen biet | Intel SHA-NI, mo rong crypto ARMv8 |
| An toan cho su dung ma hoa | Khong - khong dung cho chu ky, cert pinning, bam mat khau | Co (ngoai bam mat khau - dung Argon2id/bcrypt cho mat khau) |
Tai sao MD5 bi pha va dieu do thuc su co nghia gi
Mot va cham la hai dau vao khac nhau tao ra cung digest. Khang va cham cua MD5 da bi pha ve mat ly thuyet vao nam 2004 va thuc te vao nam 2008 - mot nha nghien cuu co the tao hai tep voi digest MD5 giong het trong vai giay tren phan cung tieu dung. Dieu nay pha vo viec MD5 dung trong chu ky so (malware Flame gia mao chu ky Windows Update vao 2012), chung chi TLS (tat ca CAs lon ngung phat hanh cert MD5 vao 2014), va bat cu boi canh nao noi mot ke thu co the anh huong dau vao.
Khang preimage thu hai cua MD5 yeu hon SHA-256 nhung khong co tan cong thuc te biet den chong lai dau vao tu y da ton tai. Do la cua so hep noi MD5 van an toan: xac nhan rang mot digest da tinh truoc khop voi mot tep ban da tai, khi khong co ke thu nao co co hoi tao va cham chong lai tep cu the do.
Khi nao MD5 van on
Tinh toan ven tep cho moi truong khong doi khang. Mot tai ISO Linux cong bo MD5 ben canh hinh anh; neu bam khop, tai cua ban khong bi hong trong qua trinh chuyen. Khong co ke thu nao tao ISO gia mao chong lai MD5 cu the do - ho can dua tep cua ho len trang upstream truoc.
Cache loai bo trung lap. Mot proxy cache lap chi muc doi tuong bang MD5 cua noi dung de phat hien lap lai. Va cham trong boi canh nay vo hai - hai doi tuong khac voi cung MD5 nghia la mot lan tuot cache, khong he qua bao mat.
Dau van tay hang co so du lieu. "Ban ghi nay co thay doi tu lan dong bo cuoi khong?" - bam MD5 hang, so sanh voi digest da luu. Nhanh hon SHA-256; mo hinh doi khang vang mat.
Dia chi noi dung Git. Git dung SHA-1 (som SHA-256), khong phai MD5 - nhung ly do thiet ke ap dung: cho mot kho luu duoc dia chi noi dung noi ban tin nguoi ghi, mot bam 128-bit du neu va cham khong la vector tan cong.
Khi nao SHA-256 la lua chon dung
Chu ky so. Chung chi TLS, ky code, ky JWT - o bat cu noi nao mot ke tan cong duoc loi tu gia mao chu ky, dung SHA-256 hoac manh hon.
Cert pinning va dau van tay khoa cong khai. Dau van tay SHA-256 cua khoa cong khai cua chung chi la tieu chuan cho pinning.
HMAC cho xac thuc tin nhan. HMAC-SHA-256 la duong co so cho ky yeu cau API (AWS Signature v4, GitHub webhooks, Stripe). HMAC-MD5 van dung trong mot so giao thuc cu nhung ngay cang bi gan co boi may quet tuan thu.
Cai gi dung cho mat khau (spoiler: khong cai nao)
Khong dung MD5 hoac SHA-256 truc tiep cho luu tru mat khau. Ca hai nhanh - dieu do xau cho mat khau. Mot ke tan cong voi digest bi ro ri co the kiem tra hang ti mat khau ung vien moi giay tren GPU. Dung mot ham bam mat khau: Argon2id (de xuat OWASP 2025), bcrypt, hoac scrypt. Cac ham nay co y cham va doi bo nho, nen mot ke tan cong chi co the kiem tra hang nghin ung vien moi giay, khong hang ti.
Thuc te hieu suat trong 2026
MD5 van ~1,7× nhanh hon SHA-256 tren CPU khong co SHA-NI. Tren CPU voi Intel SHA-NI (Goldmont+, 2017) hoac mo rong crypto ARMv8 (Cortex-A53 tro di), SHA-256 thuc su bang hoac vuot throughput MD5 - khoang cach toc do thuc day chon MD5 trong nhung nam 2000 khong con dung.
JavaScript trong trinh duyet voi WebCrypto (crypto.subtle.digest('SHA-256', data)) dat ~200 MB/s tren laptop hien dai. Cong cu chuyen doi MD5 cua chung toi chay MD5 voi toc do tuong tu qua trien khai wasm.
MD5 hoac SHA-256: quy tac ranh gioi tin cay
Lua chon giua MD5 va SHA-256 phu thuoc vao mot cau hoi duy nhat - lieu mot ke thu co the anh huong dau vao ban dang bam. Neu mot nguoi upload tu xa, mot ke tan cong mang, hoac bat ky ben nao ngoai ranh gioi tin cay cua ban co the dinh hinh cac byte den ham bam, chon SHA-256 (hoac SHA-3, hoac BLAKE3) de mot tan cong va cham khong the gia mao mot digest khop. Neu dau vao den tu pipeline cua ban va ban dang dau van tay chung cho cache, loai bo trung lap, hoac phat hien thay doi, MD5 on va chay nhanh hon mot chut tren CPU khong co SHA-NI. Quyet dinh la nhi phan va song tai ranh gioi tin cay; mot khi ban da goi ten ben nao cua ranh gioi do dau vao nam, thuat toan de dung duoc quyet dinh.
Cong cu lien quan
- MD5 Converter - tinh MD5 cua van ban hoac mot tep nho trong trinh duyet.
- Text Diff - so sanh hai khoi van ban tung dong.
- Text / HTML Editor - render HTML va Markdown truc tiep.
- Current Time (ms) - thoi gian epoch de tuong quan log.
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