Digital subtraction angiography (DSA) is referred to as DSA for short, that is, the angiographic images are digitized, unnecessary tissue images are deleted, and only vascular images are kept. This technology is called digital subtraction technology, which is characterized by clear image and high resolution. It provides a real stereoscopic image for observing vascular diseases, vascular stenosis, positioning measurement, diagnosis and interventional therapy, and provides the necessary conditions for various interventional treatments. It is mainly suitable for the examination and treatment of systemic vascular diseases and tumors. The application of DSA in interventional therapy has opened up a new field for the diagnosis and treatment of cardiovascular diseases. It is mainly used for the diagnosis and treatment of coronary heart disease, arrhythmia, valvular disease and congenital heart disease.

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Directory System Agent (directory system agent)

DSA- dynamic stability auxiliary system

DSA- Dynamic Stability Assistant System (STC-Stability Tracking Control System for short) is a kind of equipment needed by engines with high power output. Its function is to suppress the wheel slip caused by vehicle running or acceleration, so as to maintain the proper distribution of tire grip and maintain the driving stability of the vehicle.

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Digital signature algorithm

Digital signature algorithm (DSA) is a variant of the signature algorithm of Schnorr and ElGamal, and is regarded as DSS(DigitalSignature Standard) by NIST in the United States. The following parameters are applied in the algorithm:

Prime number with l bit length. L is a multiple of 64, ranging from 5 12 to1024;

Q: the prime factor of1of p-160;

G: g = h ((p- 1)/q) mod p, h satisfies H.

x:x & lt； Q and x are private keys;

Y: y = g x mod p, (p, q, g, y) is the public key;

H (x): one-way hash function. SHA (secure hash algorithm) is selected in DSS.

P, Q, G can be enjoyed by a group of users, but in practical application, using the male model may bring some threats. The signing and verification protocols are as follows:

1.p generates random numbers k, k.

2.p calculate r = (g k mod p) mod q.

s = ( k^(- 1) (H(m) + xr)) mod q

The signature result is (m, r, s).

3. Calculate w = s (- 1) mod q during verification.

u 1 = ( H( m ) * w ) mod q

u2 = ( r * w ) mod q

V = ((g u1* y U2) module p) module q

If v = r, the signature is considered valid.

DSA is a discrete logarithm problem based on integer finite field, and its security is similar to RSA. An important feature of DSA is that two prime numbers are public, so that when using other people's P and Q, you can confirm whether they are randomly generated or tampered with even if you don't know the private key. RSA algorithm doesn't work.

(it depends on what DSA you want ~ specific analysis of specific problems! )