--- name: "ipsec_ttosa" section: "3" platform: "linux" package: "openswan" version: "1:2.6.37-3+deb7u1" release: "Debian 7 (Wheezy)" platforms: ["linux"] url: "https://new.carta.tech/ipsec_ttosa" --- # ipsec\_ttosa(3) convert IPsec Security Association IDs to and from text, initialize an SA ID ## NAME ipsec\_ttosa, ipsec\_satot, ipsec\_initsaid - convert IPsec Security Association IDs to and from text, initialize an SA ID ## SYNOPSIS **#include \** **typedef struct {** **ip\_address dst;** **ipsec\_spi\_t spi;** **int proto;**\ **} ip\_said;** **const char \*ttosa(const char \*src, size\_t srclen,** **ip\_said \*sa);**\ **size\_t satot(const ip\_said \*sa, int format,** **char \*dst, size\_t dstlen);**\ **void initsaid(const ip\_address \*addr, ipsec\_spi\_t spi,** **int proto, ip\_said \*dst);** ## DESCRIPTION *Ttosa* converts an ASCII Security Association (SA) specifier into an **ip\_said** structure (containing a destination-host address in network byte order, an SPI number in network byte order, and a protocol code). *Satot* does the reverse conversion, back to a text SA specifier. *Initsaid* initializes an **ip\_said** from separate items of information. An SA is specified in text with a mail-like syntax, e.g. **esp.5a7@1.2.3.4**. An SA specifier contains a protocol prefix (currently **ah**, **esp**, **tun**, **comp**, or **int**), a single character indicating the address family (**.** for IPv4, **:** for IPv6), an unsigned integer SPI number in hexadecimal (with no **0x** prefix), and an IP address. The IP address can be any form accepted by [*ipsec\_ttoaddr*(3)](/ipsec_ttoaddr/3.md), e.g. dotted-decimal IPv4 address, colon-hex IPv6 address, or DNS name. As a special case, the SA specifier **%passthrough4** or **%passthrough6** signifies the special SA used to indicate that packets should be passed through unaltered. (At present, these are synonyms for **tun.0@0.0.0.0** and **tun:0@::** respectively, but that is subject to change without notice.) **%passthrough** is a historical synonym for **%passthrough4**. These forms are known to both *ttosa* and *satot*, so the internal representation is never visible. Similarly, the SA specifiers **%pass**, **%drop**, **%reject**, **%hold**, **%trap**, and **%trapsubnet** signify special \`\`magic'' SAs used to indicate that packets should be passed, dropped, rejected (dropped with ICMP notification), held, and trapped (sent up to [*ipsec\_pluto*(8)](/ipsec_pluto/8.md), with either of two forms of **%hold** automatically installed) respectively. These forms too are known to both routines, so the internal representation of the magic SAs should never be visible. The **\** header file supplies the **ip\_said** structure, as well as a data type **ipsec\_spi\_t** which is an unsigned 32-bit integer. (There is no consistency between kernel and user on what such a type is called, hence the header hides the differences.) The protocol code uses the same numbers that IP does. For user convenience, given the difficulty in acquiring the exact set of protocol names used by the kernel, **\** defines the names **SA\_ESP**, **SA\_AH**, **SA\_IPIP**, and **SA\_COMP** to have the same values as the kernel names **IPPROTO\_ESP**, **IPPROTO\_AH**, **IPPROTO\_IPIP**, and **IPPROTO\_COMP**. **\** also defines **SA\_INT** to have the value **61** (reserved by IANA for \`\`any host internal protocol'') and **SPI\_PASS**, **SPI\_DROP**, **SPI\_REJECT**, **SPI\_HOLD**, and **SPI\_TRAP** to have the values 256-260 (in *host* byte order) respectively. These are used in constructing the magic SAs (which always have address **0.0.0.0**). If *satot* encounters an unknown protocol code, e.g. 77, it yields output using a prefix showing the code numerically, e.g. \`\`unk77''. This form is *not* recognized by *ttosa*. The *srclen* parameter of *ttosa* specifies the length of the string pointed to by *src*; it is an error for there to be anything else (e.g., a terminating NUL) within that length. As a convenience for cases where an entire NUL-terminated string is to be converted, a *srclen* value of **0** is taken to mean **strlen(src)**. The *dstlen* parameter of *satot* specifies the size of the *dst* parameter; under no circumstances are more than *dstlen* bytes written to *dst*. A result which will not fit is truncated. *Dstlen* can be zero, in which case *dst* need not be valid and no result is written, but the return value is unaffected; in all other cases, the (possibly truncated) result is NUL-terminated. The **\** header file defines a constant, **SATOT\_BUF**, which is the size of a buffer just large enough for worst-case results. The *format* parameter of *satot* specifies what format is to be used for the conversion. The value **0** (not the ASCII character **'0'**, but a zero value) specifies a reasonable default (currently lowercase protocol prefix, lowercase hexadecimal SPI, dotted-decimal or colon-hex address). The value **'f'** is similar except that the SPI is padded with **0**s to a fixed 32-bit width, to ease aligning displayed tables. *Ttosa* returns **NULL** for success and a pointer to a string-literal error message for failure; see DIAGNOSTICS. *Satot* returns **0** for a failure, and otherwise always returns the size of buffer which would be needed to accommodate the full conversion result, including terminating NUL; it is the caller's responsibility to check this against the size of the provided buffer to determine whether truncation has occurred. There is also, temporarily, support for some obsolete forms of SA specifier which lack the address-family indicator. ## SEE ALSO [ipsec\_ttoul(3)](/ipsec_ttoul/3.md), [ipsec\_ttoaddr(3)](/ipsec_ttoaddr/3.md), [ipsec\_samesaid(3)](/ipsec_samesaid/3.md), [inet(3)](/inet/3.md) ## DIAGNOSTICS Fatal errors in *ttosa* are: empty input; input too small to be a legal SA specifier; no **@** in input; unknown protocol prefix; conversion error in *ttoul* or *ttoaddr*. Fatal errors in *satot* are: unknown format. ## HISTORY Written for the FreeS/WAN project by Henry Spencer. ## BUGS The restriction of text-to-binary error reports to literal strings (so that callers don't need to worry about freeing them or copying them) does limit the precision of error reporting. The text-to-binary error-reporting convention lends itself to slightly obscure code, because many readers will not think of NULL as signifying success. A good way to make it clearer is to write something like: ``` const char *error; error = ttosa( /* ... */ ); if (error != NULL) { /* something went wrong */ ```