P-192 (secp192r1, prime192v1) is the smallest NIST prime curve; at about 96-bit security it is legacy-only.
P-192 is a short Weierstrass curve y² = x³ + ax + b over a 192-bit prime field with a 192-bit prime-order subgroup and cofactor 1; its estimated security level is 96 bits. Status: deprecated, do not use for new keys.
P-192 is the short Weierstrass curve y² = x³ − 3x + b over the prime 2^192 − 2^64 − 1. It was standardised in FIPS 186-2 (2000), appears in SEC 2 as secp192r1 and in ANSI X9.62 as prime192v1. As with the other NIST prime curves, b was derived from the published seed with SHA-1; where the seed itself came from is not documented.
A 192-bit group gives about 96 bits of security against Pollard's rho, below the 112-bit minimum of NIST SP 800-57. NIST SP 800-186 therefore classifies P-192 as legacy-use: it may still verify existing signatures but must not sign anything new. RFC 8422 deprecated it for TLS (code point 19).